Enable the `codequality_mr_diff_annotations` feature flag by default, update documentation accordingly

What does this MR do?

Feature issue: #2526 (closed)
Feature flag issue: #330909 (closed)

This MR enables the codequality_mr_diff_annotations feature flag by default

This MR also updates the code quality in diff view documentation to reflect the new state of the inline code quality annotations feature and feature flag

⚠ Expect merge conflicts if !63461 (merged) is merged first because it removes the old feature flag

Screenshots

before	after

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.