Put Batched Suggestions behind a Feature Flag default to false

What does this MR do?

In order to prevent unpredictable and incorrect application of suggestions when using the recent Add suggestion to Batch feature, this MR disables the Add to Batch button when the line count will be changed by applying the suggestion.

Update: we ended up wrapping the UI button behind a feature flag.

Screenshots

Feature flag disabled (default)	Feature flag enabled

Outdated screenshot

This was before we switched to putting it behind a feature flag

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

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Addresses #222780 (closed)