New routes for v3.10 compatibility

[nemunaire]

In order to see the archive function to work, we need to implement the /sync/v3/check-files route.

Here is the input:

{
    "filename": "a7be6e0ea961-453b-5d54-b76e-b939beb9",
    "files": [
        "a7be6e0ea9618b3421b3131f1453b3f6e8453b5b01453bdccc7bf123b4bebeb9",
        "84eae55a21242bc1b8da64209161ed97ea2927a24ec434732d363453ab3ad9d4",
        "3d4b122055d556f2cd0e936e4dd264817e17196cb828e886cc7ae6d298268b45",
        "ebaef2a30e1d43068726d14c31b4ce763585c1f942be7cd2f8843d55f99fe6f8",
        "ba023d47bd42294fd3f64869507a96cea932b8157d14f1c315c84bba87d6e9a4"
    ],
    "reason": "Archive"
}

I also see a reason "Logout" when we try to unpair the device from cloud.

The current implementation doesn't return anything and it works. (As we didn't delete any file, the archived file can be retrieved as always.)

[nemunaire]

There is another route GET /sync/v3/missing returning {"hashes":[]}.

The route POST /sync/v3/check-files returns {"missingFiles":[]} filled with eventual missing blob id.