[Wiki] Add instructions about setting up / managing the mediation adapter extensions

[caroparo]

New users seem to get confused about SDK warnings or errors from Google Play Console. Some apps got rejected (e.g. AppLovin SDK is no longer allowed for Families games).

[Markieboyyy]

did you find an answer to this issue? because google is saying this:
com.applovin:applovin-sdk com.applovin:applovin-sdk: Consider upgrading to a policy-compliant version of the SDK if available from your SDK provider, or removing the SDK.

[BenMiller3]

Following for an update.

[caroparo]

This is a feature request for wiki update, and not a bug.

You can and should delete unwanted SDKs (e.g. AdMobAppLovin) from under the root AdMob extension. It is only a mediation adapter, and shouldn't cause a problem.

For more information on AdMob mediation adapters, please refer to
Google's official documentation for now.

In fact, if you don't use mediation at all, you should probably delete all child SDKs (AdMobAppLovin, AdMobIronSource, AdMobMeta, AdMobPangle, AdMobUnityAds) since they won't do anything without a proper setup and will only increase your build size.