codeintel: Reduce gitserver errors for missing revisions

Created by: efritz

If we hit a revision not found error in the codeintel client, we do not want to treat these as alertable errors as they are generally expected due to force-pushing over commits which codeintel holds references to.

We should move the handling of this class of errors up the stack. We still return the original error, we just don't emit a metric for it.

https://github.com/sourcegraph/sourcegraph/pull/16844 handles this error on the commit graph updater side. A future effort will need to do the same thing for the index schedulers.