[firebase_admob] Update documentation to add iOS Admob ID & add iOS Admob ID in example project

[KaYBlitZ]

Description

Update documentation to add app id in Info.plist. It is required starting in version 7.42.0. See https://firebase.google.com/docs/admob/ios/quick-start#update_your_infoplist.

Related Issues

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Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See [Contribution Guide]).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
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Breaking Change

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• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[collinjackson]

This is a documentation-only change, but we still need to update the CHANGELOG.md and pubspec.yaml. Could you please update your CL to bump 0.8.0+3 to 0.8.0+4?

[KaYBlitZ]

Hey, I updated the CHANGELOG and pubspec to +4. I also decided to add the iOS Admob App ID to the Info.plist in the example project so it won't crash on startup.

[jeffscaturro-aka]

I was just poking around seeing if we needed to throw up a PR to add this as well. Error isn't easily seen from running via flutter; we saw the actual error causing the crash when we ran through Xcode.

Anything we can do to help get this through?