fix: Implement enrollment fetch operation and add checks to validate …

[sitaram-kalluri]

…the enrollment request

- What I did

• Add enroll:fetch to return the enrollment details
• Add a validation to prevent a submission of an enrollment request with duplicate appName and deviceName.
• If an enrollment with duplicate appName and deviceName is submitted then throw an exception.

- How I did it

• Use getAtKeys with "enrollment" regex to fetch the list of keys related to enrollment.
• Iterate the List of enrollment keys and check if an enrollment with the same appName and deviceName exists. If yes, return exception.
• Add a random id to the deviceName for the existing functional tests to ensure appName and deviceName combination is unique for each enrollment request.

- How to verify it

• Added unit and functional tests to assert the changes. All tests should pass.