Handle different commit errors in IDE

What does this MR do?

This MR fixes a long lasting issue of broken error reporting in the Web IDE. Previously we always showed a "Branch changed" message, but now we actually read and parse the error message we get from the BE.

Screenshots

	Screenshot
CODEOWNERS error
Branch changed error
Unexpected error

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

References

• Related to #212595 (closed)