Swap FK dast_site_profiles_pipelines.ci_pipeline_id to ci_pipelines for LFK

What does this MR do and why?

Per &7249 (closed)

As part of our CI "decomposition" efforts we need to remove all foreign keys that are cross-database (ie. between the planned main and ci databases). We are going to replace them all with "loose foreign keys".

Related: #348272 (closed)

!77640 (merged) previously added the LFK

Validations

• Best team to review (check off when reviewed): groupdynamic analysis devopssecure
• No way for user to access once parent is deleted. Please explain: @philipcunningham FK is unused and is safe to remove because DAST table referenced by the join table is no longer used by DAST on-demand scans. Context is that the FK was added to support another scan policies but the approach changed.
• Possible to access once parent deleted but low user impact. Please explain:
• Possible Sidekiq workers that may load directly and possibly lead to exceptions. Please explain:
• Possible user impact to be evaluated or mitigated. Please explain:
• Is this FK safe to be removed to avoid LOCKing problems? (Explanation: &7249 (comment 819662046)). Please explain: We agreed that getting lock on ci_pipelines is likely

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.