ci: Generate RSpec predictive jobs dynamically

What does this MR do and why?

This generates the rspec * predictive and rspec-ee * predictive jobs dynamically in child pipelines, so that the parallelization can be set accordingly.

This leverages scripts/generate_rspec_pipeline.rb which was generalized in a previous MR.

This MR includes three distinct commits. The two first commits are pre-requisite for the last one, which is the actual child pipeline generation change.

Open questions

• Impact on Sisense metrics: Sisense metrics should already take child pipelines in account (since we already use child pipelines)
• Impact on JiHu? Should JiHu follow the same child pipeline pattern for rspec-jh * predictive jobs (if any)?

Testing matrix

Changes	Control MR	Test MR	predictive jobs created before	predictive jobs created after	Jobs saved
controller and view	!113466 (closed)	!113527 (closed)	rspec: 28 unit, 12 integration, 28 system / rspec-ee: 18 unit, 6 integration, 10 system	rspec: 1 unit, 1 integration, 2 system; rspec-ee: 1 integration, 1 system	102

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.