refactor: dcr logics into ims-go library

[Eiermitsucuk]

Description

Adds Dynamic Client Registration (DCR) support to the ims-go library. The DCR logic that previously lived in imscli has been moved into ims-go, making it reusable as a proper library concern. imscli now only handles command parsing and delegates all registration logic to ims-go.

Motivation and Context

By moving the logic into ims-go, the library becomes the single source of truth for DCR. imscli is now a thin CLI layer — it parses flags and calls into ims-go, nothing more. This separation makes the codebase easier to maintain and the library more useful on its own.

How Has This Been Tested?

• Manually ran ./imscli dcr register end-to-end against the Adobe IMS endpoint to verify the command still works after the refactor
• Confirmed that removing the logic from imscli did not break existing command behavior
• Verified error handling (missing parameters, bad URLs) is correctly propagated from ims-go up to the CLI layer

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)