feat: add distribution API (with bug fix)

[pendo324]

Issue #, if available:

Description of changes

This is largely the same as #92, but with e2e tests added, and a small diff for a bugfix and to conform to the status codes returned by other existing implementations.

• Adds the Distribution API, as documented here https://docs.docker.com/reference/api/engine/version/v1.43/#tag/Distribution
• Refactored some code out of the Image service as it was useful for the new Distribution service as well
• Regenerating mocks caused minor diffs in 2 existing files (reordering/adding whitespace)

Testing done

• Unit tests for new API handler (76%) and service (85%)
• e2e tests, including auth/unauth scenarios
• Manual testing using docker-py, and comparison to other implementations

Contribution agreement

• I've reviewed the guidance in CONTRIBUTING.md

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[swagatbora90]

Thanks for adding the e2e tests.