[PULP-1045] Add support for serving superseded publications for a retention period

[pedro-psb]

Introduces a DistributedPublication model to track which publications are associated with each distribution. When a new publication becomes the latest for a repository, older ones are retained and served by the content handler for a configurable grace period, allowing clients to continue fetching from superseded publications without interruption.

Handles publications with pass-trough=True|False. The behavior is sumarized:

Given:

• CA=ContentArtifact,
• PA=PublishedAritfact
• PU=Publication
• RV=RepositoryVersion
• DP=DistributedPublication
• DT=Distribution

Then CA is retrieved with:

• pass-through: CA<-PA<-PU<-DP->DT
• no-pass-through: CA<-RV<-PU<-DP->DT

Closes: #7514

📜 Checklist

• Commits are cleanly separated with meaningful messages (simple features and bug fixes should be squashed to one commit)
• A changelog entry or entries has been added for any significant changes
• Follows the Pulp policy on AI Usage
• (For new features) - User documentation and test coverage has been added

See: Pull Request Walkthrough

[mdellweg]

Can you make sure this doesn't collide with https://github.com/pulp/pulp_deb/blob/main/pulp_deb/app/models/publication.py#L136
And maybe coordinate an effort to superseed it there?

[pedro-psb]

Can you make sure this doesn't collide with https://github.com/pulp/pulp_deb/blob/main/pulp_deb/app/models/publication.py#L136

I've tested with pulp_deb running alogside. There was a collision with the reverse relationship name, then I've simply renamed the reverse relationship. I'll create a test PR on deb to be sure.

And maybe coordinate an effort to superseed it there?

Yes, I'll open an issue there and start a conversation.

[pedro-psb]

The test PR is fine: pulp/pulp_deb#1429

[pedro-psb]

I've opened the issue for the superseeding with some options: pulp/pulp_deb#1430

[pedro-psb]

I want a review of this, but I'd like pulp_deb folks feedback (on the general operation) before merging.