fix: Add retry logic in "_waitForPkamAuthSuccess" to retry when secondary is temporarily not reachable

[sitaram-kalluri]

- What I did

• After submitting an enrollment request, retry for couple of times when secondary server is temporarily not reachable.

- How I did it

• Introduce a new variable "_maxActivationRetries" which is a final variable which represents the maximum retries
• In "_waitForPkamAuthSuccess" method, catch if an exception is thrown and increment the "retryCounter" until it "maxActivationRetry" is reached. After that re-throw the exception.
• In the _attemptPkamAuth method, if enrollment is denied, it returns an AtEnrollmentException. This exception is caught in the catch block of _waitForPkamAuthSuccess (which calls _attemptPkamAuth), triggering the retry logic that we want to avoid. To prevent this, we need to handle AtEnrollmentException separately here, which introduces code duplication.
• To handle all the exceptions in one place, moved the existing exception handing logic in _attemptPkamAuth here. With the changes, _attemptPkamAuth do not handle exception. It rethrows and all the exceptions are handled in the _waitForPkamAuthSuccess.

- How to verify it

• Tested the changes manually and attaching the test log:

/usr/lib/dart/bin/dart --enable-asserts --no-serve-devtools /home/sitaram/IdeaProjects/atsign/core/at_libraries/packages/at_onboarding_cli/bin/activate_cli.dart enroll -s ABC123 -n wavi:rw -p wavi -a @alice🛠 -r vip.ve.atsign.zone -k ~/.atsign/keys/@alice-pkam-local.atKeys -d local-17
Submitting enrollment request
Waiting for approval; will check every 10 seconds
Checking ... Enrollment ID: 0d387d23-e38d-4404-b297-f11adfdd1685
 not approved. Will retry in 10 seconds
Checking ...  not approved. Will retry in 10 seconds
Checking ...  not approved. Will retry in 10 seconds
Checking ... SEVERE|2024-10-07 15:36:23.447566|OnboardingCli|Exception occurred when authenticating the atSign: @alice🛠 caused by HandshakeException: Connection terminated during handshake. Attempting to retry for 1 attempt 
 not approved. Will retry in 10 seconds
Checking ... SEVERE|2024-10-07 15:36:33.462455|OnboardingCli|Exception occurred when authenticating the atSign: @alice🛠 caused by HandshakeException: Connection terminated during handshake. Attempting to retry for 2 attempt 
 not approved. Will retry in 10 seconds
Checking ... SEVERE|2024-10-07 15:46:06.025958|OnboardingCli|Exception occurred when authenticating the atSign: @alice🛠 caused by HandshakeException: Connection terminated during handshake. Attempting to retry for 3 attempt 
 not approved. Will retry in 10 seconds
Checking ... SEVERE|2024-10-07 15:46:16.032858|OnboardingCli|Exception occurred when authenticating the atSign: @alice🛠 caused by HandshakeException: Connection terminated during handshake. Attempting to retry for 4 attempt 
 not approved. Will retry in 10 seconds
Checking ... SEVERE|2024-10-07 15:46:26.040091|OnboardingCli|Exception occurred when authenticating the atSign: @alice🛠 caused by HandshakeException: Connection terminated during handshake. Attempting to retry for 5 attempt 
 not approved. Will retry in 10 seconds
Checking ... SEVERE|2024-10-07 15:46:36.047084|OnboardingCli|Exception occurred when authenticating the atSign: @alice🛠 caused by HandshakeException: Connection terminated during handshake Activation failed after 5 attempts 
[Error] HandshakeException: Connection terminated during handshake
[Error] Enrollment failed.
  Cause: HandshakeException: Connection terminated during handshake
  Please try again or contact support@atsign.com

Process finished with exit code 0

- Description for the changelog

• fix: Add retry logic in "_waitForPkamAuthSuccess" to retry when secondary is temporarily not reachable