Fixes #14807 - don't generate repo metadata when nothing was synced

[tstrachota]

Turns off auto-publishing for yum repos in Pulp. Auto-publish always triggers metadata regenerate regardless of whether any updates are synced.

This PR adds action Pulp::Repository::Publish which conditionally publishes repos only if new content was downloaded.

DO NOT MERGE YET - tests are still missing

[jlsherrill]

@tstrachota this was filed against a version when we generated node metadata and would sync that to the capsules every time. The current syncing mechanism uses the normal yum metadata which they have optimizations on to not regenerate if nothing changed I believe. I this this issue may be solved already.

[tstrachota]

@jlsherrill from what I tested the metadata are always regenerated also in the latest version. Or at least timestamps on the files change.

[jlsherrill]

@tstrachota yeah the metadata generate action still occurs, but (at least for yum) there is some optimization so its really quick (and yum is the only one that normally takes a long time).

You should be able to test this yourself. Sync a large-ish repo and monitor 'pulp-admin tasks' to see how long the publish task takes. Sync it a 2nd time and see how long it takes.

Previously we were using the pulp node feature to sync to the capsules and i bet that ignored the optimization that we have today.

[tstrachota]

@jlsherrill ok, I'll need to try that, thanks!

[tstrachota]

Closing the PR per discussion with @jlsherrill