feat: add new method to fetch enrollment requests

[srieteja]

closes #1198

- What I did

• feat: add new method fetchEnrollmentRequests() to AtClientImpl
• test: add unit test
• refactor: minor refactoring in RemoteSecondary -> (1) simplify the notation of creating a SecureSocketConfig instance (2) removed logs in RemoteSecondary.executeAndParse() which are a duplicate of the logs in executeVerb()

- How I did it

• fetch enroll requests: do an enroll:list on the remoteSecondary and handle the information from the server and return it as a Map<String, dynamic>

- How to verify it

• added unit test should verify the functioning of the method

- Description for the changelog

feat: add new method to fetch enrollment requests

[sitaram-kalluri]

Please add functional tests to assert the changes

[sitaram-kalluri]

Add fromJson and toJson to "EnrollmentRequest" class instead of setting in for loop.

EnrollmentRequest enrollmentRequest = EnrollmentRequest.fromJson(enrollRequest);

[srieteja]

these methods have been introduced as part of 17863da

[srieteja]

This implementation has been moved to a diff pr #1222