Add toggle for spp_repository_pipeline_access in project settings

What does this MR do and why?

This MR adds a new project setting for Security Policy Projects to enable access for pipeline execution policy configurations to be fetched.

This allows users to run pipelines with PEP even if they don't have access to the repository with pipeline config.

It depends on Add setting for projects to access SPP reposito... (!164918 - merged) and Make the project setting spp_repository_pipelin... (!165190 - merged).

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Screenshots or screen recordings

For normal project	For security policy project	Setting locked by the group

How to set up and validate locally

1. Go to a project in a group, Secure -> Policies and create a new policy
2. In the created Security Policy Project, go to Settings -> General
3. A new setting should become available
4. Make a change to the setting and verify that it gets persisted
5. For the group, update the namespace setting and lock it:

   Project.find(<project-id>).group.namespace_settings.update!(spp_repository_pipeline_access: true, lock_spp_repository_pipeline_access: true)

6. Verify that the project setting toggle is disabled

Related to #469439 (closed)