Refactor response creation in API and add ingestion to pkg/version/metadata

[MagielBruntink]

Description

• Created a Responses class that creates repeating HTTP response entity objects.
• Refactor most reponse creation instances to use methods of the new class.
• Added ingestion behavior to the package/version/metadata endpoint.

Motivation and context

In our integration with FASTEN, we need ingestion to trigger on a package/version/metadata endpoint query, if the package-version is missing.

Testing

• Unit tests succeed.

Task list

• [x] DC test
• [ ] Alignment with on-going refactoring by @proksch
• [x] Resolve that some endpoints package/version are dysfunctional due to recent refactoring (see issue #500).

[MagielBruntink]

Tests with DC successful, ingestion is now triggerred for the {package}/{version}/metadata endpoint. Other endpoints also still work :-)

Also confirmed: due to issue #500 the {package}/{version} endpoint is currently broken for Debian.

[MagielBruntink]

HI @proksch @mir-am , could you please indicate when you could have time to look at this PR?

[mir-am]

HI @proksch @mir-am , could you please indicate when you could have time to look at this PR?

Hi @MagielBruntink, Actually, I wanted to review the PR this morning. I'll do it now.