Add desktop Debug provider for App Check

[a-maurice]

Description

Provide details of the change, and generalize the change in the PR title above.

Add the desktop implementation of the debug provider for App Check, which uses the desktop rest implementation to retrieve a valid attestation token from the server.

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Testing

Describe how you've tested these changes. Link any manually triggered Integration tests or CPP binary SDK Packaging Github Action workflows, if applicable.

Local testing

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Type of Change

Place an x the applicable box:

• Bug fix. Add the issue # below if applicable.
• New feature. A non-breaking change which adds functionality.
• Other, such as a build process or documentation change.

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Notes

• Bug fixes and feature changes require an update to the Release Notes section of release_build_files/readme.md.
• Read the contribution guidelines CONTRIBUTING.md.
• Changes to the public API require an internal API review. If you'd like to help us make Firebase APIs better, please propose your change in a feature request so that we can discuss it together.

[github-actions]

❌  Integration test FAILED

Requested by @a-maurice on commit 8785d02
Last updated: Mon Dec 12 16:09 PST 2022
View integration test log & download artifacts

Failures	Configs
firestore	[TEST] [FLAKINESS] [Android] [2/3 os: ubuntu windows] [1/2 android_device: android_target] (1 failed tests)   CRASH/TIMEOUT
gma	[TEST] [FAILURE] [iOS] [macos] [1/2 ios_device: ios_target] (2 failed tests)   FirebaseGmaTest.TestRewardedAdLoad   FirebaseGmaTest.TestRewardedAdLoadEmptyRequest [TEST] [FLAKINESS] [Android] [1/3 os: ubuntu] [1/2 android_device: android_target] (2 failed tests)   FirebaseGmaTest.TestInterstitialAdStress   FirebaseGmaTest.TestRewardedAdStress [TEST] [FLAKINESS] [Android] [1/3 os: windows] [1/2 android_device: android_target] (1 failed tests)   CRASH/TIMEOUT
messaging	[TEST] [ERROR] [Android] [1/3 os: windows] [1/2 android_device: android_target]
storage	[TEST] [FLAKINESS] [Android] [1/3 os: ubuntu] [1/2 android_device: android_target] (1 failed tests)   CRASH/TIMEOUT

Add flaky tests to go/fpl-cpp-flake-tracker