Improve documentation `spp_repository_pipeline_access` settings

Martin Cavojrequested to merge
487924-improve-documentation-for-spp_repository_pipeline_access-project-setting into master

What does this MR do and why?

This change is a follow-up on technical writing suggestions from !165626 (merged) to improve documentation and wording for the project setting spp_repository_pipeline_access.

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Related to #487924 (closed)

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