Add ad provider

[ulyanas]

The task is to add one more ad provider. Provider name: base

API: https://www.base.org/api/ocsRegistry Endpoints:

• GET /entries
• GET /featured

Fields mapping:

Image banners: Destination URL -> Target URL + utm_source=blockscout&utm_medium=ad Image > Image URL (looks like we don't know the dimensions yet, will probably need to resize it to fit the placements Alternate text > CTA Text

Notes:

• This ad provider should be mixable with one other (Slise).
• Since Blockscout doesn't have featured placements, we should fetch ads from both endpoints

Text ads:

Logo > Creator Image URL Name > Title Text > Short Description CTA > CTA Text Destination URL -> Target URL + utm_source=blockscout&utm_medium=ad

API spec - on request