Update compliance pipeline migration banner

What does this MR do and why?

Update wording of the compliance pipeline to pipeline execution policy migration banner, also update the link to the new docs https://docs.gitlab.com/ee/user/group/compliance_pipelines.html#pipeline-execution-policies-migration

MR acceptance checklist

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Before	After

How to set up and validate locally

1. Enable feature flag ff_compliance_pipeline_maintenance_mode in rails console (rails c): Feature.enable :ff_compliance_pipeline_maintenance_mode
2. Visit compliance center Docs
3. Create a framework which uses pipeline configuration path
4. Save framework, enter editing of this framework
5. Click 'Migrate pipeline to a policy'
6. Observe prefilled form
7. Create merge request
8. Observer description includes absolute url

Related to #440149 (closed)