Summary: Changed PathStyleAccess from a feature flag to a runtime config flag (global) when creating a Amazon S3 backup.

Test Plan: To test whether the toggle shows up in the S3 backup UI when the config flag is turned on and off.

Reviewers: vkumar, kkannan

Reviewed By: kkannan

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D41436