Skip re-upload of unchanged metadata artifacts on creating a publication

[Moustafa-Moustafa]

PublishedMetadata.create_from_file() unconditionally saved artifacts to storage on every publish. When a publication was created for an already-published repository version, this overwrote identical metadata blobs with new timestamps, causing problems with CDN caching layers that use last-modified times.

Applied the same deduplication pattern used for content artifact uploads: look up the artifact by checksum first, verify the file exists in storage, and skip the write if it does.

closes #7344

📜 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

[gerrod3]

@Moustafa-Moustafa Can you rebase with changes from main? That should fix the CI issues.

[Moustafa-Moustafa]

@Moustafa-Moustafa Can you rebase with changes from main? That should fix the CI issues.

Thanks, Done.

[gerrod3]

Looks good.

[patchback]

Backport to 3.63: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.63/862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc/pr-7346

Backported as #7460

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.49: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.49/862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc/pr-7346

Backported as #7462

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.85: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.85/862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc/pr-7346

Backported as #7459

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.105: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.105/862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc/pr-7346

Backported as #7461

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.73: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.73/862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc/pr-7346

Backported as #7463

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.73: 💔 creation of the backport PR failed

❌ Backport PR branch: patchback/backports/3.73/862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc/pr-7346

Validation Failed: 'A pull request already exists for pulp:patchback/backports/3.73/862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc/pr-7346.'

Backporting merged PR #7346 into main

1. Ensure you have a local repo clone of your fork. Unless you cloned it
   from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these
   instructions you'll refer to it by the name upstream. If you don't
   have it, here's how you can add it:

   $ git remote add upstream https://github.com/pulp/pulpcore.git

3. Ensure you have the latest copy of upstream and prepare a branch
   that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/3.73/862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc/pr-7346 upstream/3.73

4. Now, cherry-pick PR Skip re-upload of unchanged metadata artifacts on creating a publication #7346 contents into that branch:

   $ git cherry-pick -x 862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc

   If it'll yell at you with something like fatal: Commit 862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc is a merge but no -m option was given., add -m 1 as follows instead:

   $ git cherry-pick -m1 -x 862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR Skip re-upload of unchanged metadata artifacts on creating a publication #7346 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.73/862e1c2209d7a5efb30d3d585b362c4ef5e5b3cc/pr-7346

7. Create a PR, ensure that the CI is green. If it's not — update it so that
   the tests and any other checks pass. This is it!
   Now relax and wait for the maintainers to process your pull request
   when they have some cycles to do reviews. Don't worry — they'll tell you if
   any improvements are necessary when the time comes!

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.