fix: Pin Google Play Services Ads to 22.6.0

[shinwan2]

Summary

This fixes the build failure when building PrebidDemoKotlin for example. Below is the failure log

Manifest merger failed : uses-sdk:minSdkVersion 19 cannot be smaller than version 21 declared in library [com.google.android.gms:play-services-ads:23.0.0] /Users/shinwan2/.gradle/caches/transforms-3/81f307a4ec7ff1c69519d0f953072760/transformed/jetified-play-services-ads-23.0.0/AndroidManifest.xml as the library might be using APIs not available in 19
  Suggestion: use a compatible library with a minSdk of at most 19,
    or increase this project's minSdk version to at least 21,
    or use tools:overrideLibrary="com.google.android.gms.ads.impl" to force usage (may lead to runtime failures)

This is because the version was not pinned

implementation 'com.google.android.gms:play-services-ads:+'

and Google has released version 23.0.0 on 2024-03-07 which changes the minimum Android API level to 21 while Prebid still requires minimum API level 19.

I use version catalog to centralize the constant. Let me know if a naming convention for that exists.

Test

Run the demo app.

[jsligh]

This solves the problem currently but this issue needs to be further researched / addressed: #744

[jsligh]

Temporarily solves the issue but see linked issue for future things for us to work on.