Rebase fails with "something went wrong" and huge ugly conflict error.

After clicking the rebase button we see a "something went wrong" error.

It looks like we are revealing too much internal info here as well as failing to catch this error on the ui.

gitlab.com.har

Changes in scope for the fix in this issue:

• Remove the red banner message at the top when encountering this error.
• The red message in the widget should be replaced with: Rebase failed. Please rebase locally..
• If rebase failed due to conflicts, add a note saying: Rebase failed. This is most likely due to conflicts. Please rebase locally.