MergeRequest#rebase_in_progress? and MergeRequest#rebase_path were called
twice each time per request. This memoization helps reduce the overall number
of queries.

See https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/51616319 as a failing
job.

Closes gitlab-org/gitlab-ee#4857

This reduces the number of RefExists RPC call.

+ address small nitpicks

- Move the exception handling as close to the source as possible to
avoid leaking Psych ahstraction
- Also remove unnecessary rescue all statement from LintsController.
This should not be necessary anymore since any YAML errors should all be
caught by the #validation_message method.

Signed-off-by: Bastian Blank <waldi@debian.org>

it will also automatically prune empty directories for
`FileUploader`-based uploaders.

Removing last_sign_in_at in specs

Fixes #32282.

Currently we still need to run EnsureStageService within a transaction,
because when it runs within in a transaction we are going to stick to
the primary database when using database load balancing. Extracting this
out of the transaction makes it possible to hit into problems with
replication lag in pipeline commit status API, which can cause a lot of
trouble.