Reintroduce auto_explain query recording for default ref pipelines

What does this MR do and why?

This enables the recording of database queries using auto_explain in CI pipelines. As of Capture queries during rspec using pg auto_explain (!125454 - merged) being merged, these were only recorded for merged result pipelines when certain labels are present, this adds if-default-branch-refs in order to generate a canonical report of queries to compare against in future MRs.

This was originally merged in !128862 (merged) which was reverted due to an unintentional effect on docs only pipelines.

The issue with docs only pipelines is fixed in 473e4193c99ef9961a1e9b4bd377cc3d937037e5 based on a suggestion from @rymai.

Since there is no way to test this without merging, we should merge, then watch the next docs pipeline, and be prepared to revert this MR if needed.

Relates to #422106 (closed)

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