functional tests for APKAM in at_client/onboarding_cli

[murali-shris]

Is your feature request related to a problem? Please describe.

we currently have few functional tests in at_onboarding_cli for APKAM enrollment,auth, usage of get/put/scan etc.,
https://github.com/atsign-foundation/at_libraries/blob/apkam_onboarding_changes_squashed/tests/at_onboarding_cli_functional_tests/test/enrollment_test.dart
We need a comprehensive set of end2end tests in at_client for APKAM

Describe the solution you'd like

Tests should cover

• onboarding+enrollment of first client (so the first client can approve future enrollment requests)
• enrollment submission of new client
• invalid OTP from new enrollment request
• re-use of valid OTP more than once should be prohibited
• OTPs after timeout should be invalid
• enrollment approval/deny/timeout
• client side functionalities after enrollment put,get, scan,llookup etc.,
• enrolled client should not be able to access unauthorized namespaces

Describe alternatives you've considered

No response

Additional context

No response

[murali-shris]

Updates in PR 75:

• Added two demo atsigns to virtual environment. Minor changes done in virtual env setup
  https://github.com/atsign-foundation/at_server/tree/virtual_env_changes_apkam
• Took up refactoring change in at_auth package
  feat: enrollment code changes for reusability between at_client_mobile and at_onboarding_cli at_libraries#461
  Tested onboarding_cli tests using local virtual environment
• Tests in at_client to be wrapped up in PR76.

[murali-shris]

Functional tests changes are in apkam_onboarding_changes branch. Took a task to explore appium for at_client_mobile testing.