`adUnit.ortbConfig` can not customize OpenRTB objects like `/imp[].video.api`

[takenorim]

Describe the bug Unlike GAM oringial integration API (e.g. VideoParameters.java), other integration types (e.g. AdMob integration) does not provide basic setter methods (e.g. setApi) to customize OpenRTB params.

I can customize some of OpenRTB objects (e.g. /bidfloor, /app.content.cat) via adUnit.ortbConfig. However, I have difficulty to customize any OpenRTB objects inside the /imp[] array (e.g. /imp[].video.api, /imp[].video.protocols, etc).

To Reproduce Based on the demo app AdMobVideoInterstitialActivity.kt, I tried to use the adUnit.ortbConfig to add /imp[0].video.api: [5,6,7], but all of them does not work as I expected. See Additional context section below for more detail.

Expected behavior There should be a method to customize OpenRTB objects like /imp[].video.api, /imp[].video.mimes, /imp[].banner.pos and so on for generic integration types.

Additional context Testing adUnit.ortbConfig as below.

1. adUnit?.ortbConfig = "{\"imp\":[{\"video\":{\"api\":[5,6,7]}}]}" Then, POST payload to Prebid Server is below.

   {
   "imp": [
   {
     "id": "ede891f1-4f70-4ce4-b26c-91844397d3c5",
     "displaymanager": "prebid-mobile",
     "displaymanagerver": "2.2.3",
     "instl": 0,
     "clickbrowser": 0,
     "video": {
       "mimes": [
         "video/mp4",
         "video/3gpp",
         "video/webm",
         "video/mkv"
       ],
       "playbackend": 2,
       "protocols": [
         2,
         5
       ],
       "w": 393,
       "h": 759,
       "linearity": 1,
       "placement": 5,
       "delivery": [
         3
       ],
       "pos": 7
     },
     "ext": {
       "prebid": {
         "storedrequest": {
           "id": "prebid-demo-video-interstitial-320-480"
         }
       }
     }
   },
   {
     "video": {
       "api": [
         5,
         6,
         7
       ]
     }
   }
   ],
   "id": "ede891f1-4f70-4ce4-b26c-91844397d3c5",
   "app": {
   "name": "Prebid Kotlin Demo",
   "bundle": "org.prebid.mobile.prebidkotlindemo",
   "ver": "1.0.0",
   "publisher": {
     "id": "0689a263-318d-448b-a3d4-b02e8a709d9d"
   },
   "ext": {
     "prebid": {
       "source": "prebid-mobile",
       "version": "2.2.3"
     }
   }
   },
   "device": {
   "ua": "Mozilla/5.0 (Linux; Android 14; sdk_gphone64_arm64 Build/UE1A.230829.036.A1; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/113.0.5672.136 Mobile Safari/537.36",
   "lmt": 0,
   "devicetype": 4,
   "make": "Google",
   "model": "sdk_gphone64_arm64",
   "os": "Android",
   "osv": "14",
   "hwv": "Google sdk_gphone64_arm64",
   "language": "en",
   "ifa": "1336c7ac-2b2e-490c-9cae-10ca1ad1abe1",
   "h": 2220,
   "w": 1080,
   "connectiontype": 2,
   "pxratio": 2.75
   },
   "regs": {
   "ext": {
     "gdpr": 1
   }
   },
   "user": {},
   "source": {
   "tid": "ede891f1-4f70-4ce4-b26c-91844397d3c5",
   "ext": {
     "omidpv": "2.2.3",
     "omidpn": "Prebid"
   }
   },
   "ext": {
   "prebid": {
     "storedrequest": {
       "id": "0689a263-318d-448b-a3d4-b02e8a709d9d"
     },
     "targeting": {}
   }
   }
   }

2. adUnit?.ortbConfig = "{\"imp\":{\"video\":{\"api\":[5,6,7]}}}" Then, POST payload (omit irrelevant objects like /app, device) to Prebid Server is below.

   {
   "imp": [
   {
     "id": "bea60f7c-259f-408a-bf28-ecd390ae83b2",
     "displaymanager": "prebid-mobile",
     "displaymanagerver": "2.2.3",
     "instl": 0,
     "clickbrowser": 0,
     "video": {
       "mimes": [
         "video/mp4",
         "video/3gpp",
         "video/webm",
         "video/mkv"
       ],
       "playbackend": 2,
       "protocols": [
         2,
         5
       ],
       "w": 393,
       "h": 759,
       "linearity": 1,
       "placement": 5,
       "delivery": [
         3
       ],
       "pos": 7
     },
     "ext": {
       "prebid": {
         "storedrequest": {
           "id": "prebid-demo-video-interstitial-320-480"
         }
       }
     }
   }
   ],
   "id": "bea60f7c-259f-408a-bf28-ecd390ae83b2",
   ...(snip)...
   }

3. adUnit?.ortbConfig = "{\"imp[0]\": {\"video\":{\"api\":[5,6,7]}}}" Then, POST payload (omit irrelevant objects like /app, device) to Prebid Server is below.

   {
   "imp": [
   {
     "id": "acc228ac-7e5e-4e08-89ef-f03b7a6f28bf",
     "displaymanager": "prebid-mobile",
     "displaymanagerver": "2.2.3",
     "instl": 0,
     "clickbrowser": 0,
     "video": {
       "mimes": [
         "video/mp4",
         "video/3gpp",
         "video/webm",
         "video/mkv"
       ],
       "playbackend": 2,
       "protocols": [
         2,
         5
       ],
       "w": 393,
       "h": 759,
       "linearity": 1,
       "placement": 5,
       "delivery": [
         3
       ],
       "pos": 7
     },
     "ext": {
       "prebid": {
         "storedrequest": {
           "id": "prebid-demo-video-interstitial-320-480"
         }
       }
     }
   }
   ],
   "id": "acc228ac-7e5e-4e08-89ef-f03b7a6f28bf",
   
   ...(snip)...
   
   "imp[0]": {
   "video": {
     "api": [
       5,
       6,
       7
     ]
   }
   }
   }

4. adUnit?.ortbConfig = "{imp[0].video.api=[5,6,7]}" Then, POST payload (omit irrelevant objects like /app, device) to Prebid Server is below.

   {
   "imp": [
   {
     "id": "8614a9a5-0cd3-455e-8f79-b710b243f6cd",
     "displaymanager": "prebid-mobile",
     "displaymanagerver": "2.2.3",
     "instl": 0,
     "clickbrowser": 0,
     "video": {
       "mimes": [
         "video/mp4",
         "video/3gpp",
         "video/webm",
         "video/mkv"
       ],
       "playbackend": 2,
       "protocols": [
         2,
         5
       ],
       "w": 393,
       "h": 759,
       "linearity": 1,
       "placement": 5,
       "delivery": [
         3
       ],
       "pos": 7
     },
     "ext": {
       "prebid": {
         "storedrequest": {
           "id": "prebid-demo-video-interstitial-320-480"
         }
       }
     }
   }
   ],
   "id": "8614a9a5-0cd3-455e-8f79-b710b243f6cd",
   ...(snip)...
   }