Summary:
Original commit: 90072533aa623748b5d34bbf9a60fd927f009be3 / D39212
Convert to normal gFlag instead of Preview.
Flag is still kept OFF by default, since turning it on will case pg_cron launcher to run even if the extension is not created by the user.

Fixes #24523
Jira: DB-13555

Test Plan: Jenkins

Reviewers: tnayak, fizaa, slingam

Reviewed By: fizaa

Subscribers: ybase

Differential Revision: https://phorge.dev.yugabyte.com/D39423