Use SaaS metadata helper in foss

What does this MR do and why?

• Moves the :saas metadata helper(ee/spec/support/stub_dot_com_check.rb) to ce as we have code that could use it there and is valid to have.
• Resolves easily resolvable specs to use it in ce. Leaves the specs that stub it(:com?) with a variable or explicit toggling alone.
• Changes some context/example descriptions to reflect SaaS instead of gitlab.com for more alignment on the concept of saas. Left others alone based on the context of file/tests around it.

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.

Relates to #378167