Validate fields in enrollment requests

[murali-shris]

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

Currently not all mandatory fields in enrollment request are validated

Describe the solution you'd like

• document and review fields in enrollment requests for all enroll commands
• implement the validations

Describe alternatives you've considered

No response

Additional context

No response

[murali-shris]

Mandatory fields: enroll:request

• app name
• device name
• namespaces - atleast one
• apkam public key
• encrypted apkam symmetric key

enroll:approve

• enrollmentId
• encrypted default encryption private key
• encrypted default self encryption key

enroll:revoke / enroll:deny / enroll: fetch

• enrollmentId

[murali-shris]

Pull request pending review and merge https://github.com/atsign-foundation/at_server/pull/2001