Default enable FF enable_environments_search_within_folder

What does this MR do and why?

Default enable FF as we have validated on gitlab.com for more than 5 days now without concerns.

Observed to be fine from the logs:

• https://log.gprd.gitlab.net/goto/f821afd0-6b01-11ed-9f43-e3784d7fe3ca
• https://log.gprd.gitlab.net/goto/9afdcdd0-6b00-11ed-85ed-e7557b0a598c (Created #384044 (closed) to capture the errors noticed in these logs which are not related to this FF)

FF issue: #382108 (closed)

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.

Related to #373850 (closed)