Summary:
This diff enables on-prem provider server-side validation by default and standardizes
the validation controls to runtime config only by removing the AWS provider validation
feature flag from the `/features` page.

Test Plan:
Test provider validation for AWS and on-prem providers manually.
UI itest.
{F409546}
{F409547}

Reviewers: nsingh, rmadhavan, kkannan, lsangappa

Reviewed By: nsingh

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D47947