Optimise cleaning up LFS objects

What does this MR do?

The GetAllLfsPointers RPC is quite expensive, and we're running as part of GitGarbageCollectWorker as well as manually.

Since all it does is remove links between Project and LfsObject, we can skip running it at-all if the project has 0 LFS objects linked.

We can also catch and log errors so that gc won't be negatively affected if a timeout does occur here.

Another option would be to split it out into another worker entirely, which might be a touch clearer, but I'll leave that decision to reviewer/maintainer.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Part of #238605 (closed)