Replace existing Feature Flags with a single of OPS type

What does this MR do?

Implements #266986 (closed)
We want to keep a single Feature Flag for Image Resizing, and it will be an OPS type, as we expect to keep it for a longer time (at least until 13.7).

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

N/A

Related to #266986 (closed)