Add datasource for Firebase Android App Config

[rainshen49]

Add a data source for Firebase Android App Config. Similar to firebase_apple_app_config

If this PR is for Terraform, I acknowledge that I have:

• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
• Ran relevant acceptance tests using my own Google Cloud project and credentials (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

firebase_android_app_config

[c2thorn]

/gcbrun

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 2 files changed, 2 insertions(+))
Terraform Beta: Diff ( 3 files changed, 214 insertions(+))

[modular-magician]

Tests analytics

Total tests: 2547
Passed tests 2268
Skipped tests: 275
Affected tests: 4

Action taken

Found 4 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccComputeForwardingRule_update|TestAccApigeeKeystoresAliasesKeyCertFile_apigeeKeystoresAliasesKeyCertFileTestExample|TestAccApigeeEnvKeystoreAliasPkcs12_apigeeEnvKeystoreAliasPkcs12Example|TestAccDataSourceGoogleFirebaseAndroidAppConfig

Get to know how VCR tests work

[modular-magician]

Tests passed during RECORDING mode:
TestAccComputeForwardingRule_update[Debug log]
TestAccApigeeKeystoresAliasesKeyCertFile_apigeeKeystoresAliasesKeyCertFileTestExample[Debug log]
TestAccApigeeEnvKeystoreAliasPkcs12_apigeeEnvKeystoreAliasPkcs12Example[Debug log]
TestAccDataSourceGoogleFirebaseAndroidAppConfig[Debug log]

All tests passed
View the build log or the debug log for each test

[rileykarson]

@c2thorn: Watch out for the resource name in the changelog, this one was left unticked! https://github.com/GoogleCloudPlatform/magic-modules/blob/main/.ci/RELEASE_NOTES_GUIDE.md#unticked-resource-names

[rainshen49]

I forgot to add documentation here. It is being added in #8457