Migrate AndroidKeyManager to web5-kt

[michaelneale]

Similar to AWSKeyManager there is an AndroidKeyManager implementation currently in the android example: https://github.com/TBD54566975/tbdex-android-example/blob/main/app/src/main/kotlin/AndroidKeyManager.kt and a test for it here: https://github.com/TBD54566975/tbdex-android-example/blob/main/app/src/androidTest/kotlin/AndoidKeyManagerTest.kt

It may make sense to move this into web5-kt similar how AWSKeyManager is in there.

Some considerations:

• Don't want to bring in the android libraries for non android projects
• Want to build with android libraries
• Need to test with Android environment (a github action in the example project shows how: https://github.com/TBD54566975/tbdex-android-example/blob/main/.github/workflows/integration.yml)

cc @ALRubinger for thoughts on packaging and testing.

[ALRubinger]

Packaging, testing, bringing it together: #287