Allow bootsnap to be configured

What does this Merge Request do and why?

This MR adds a new setting called gitlab.rails.bootsnap that allows Bootsnap to be enabled (by default) or disabled.

Related: gitlab!73331 (merged)

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.