Save MR description when changing target branches in create mode
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# Problem:
1. I create a branch B from branch A in the terminal
1. I push the branch and I get the MR link in the terminal
1. I click it and it opens the MR create page
1. I fill in the data (title and description, scroll down and then notice that the target branch is master, however I want to merge against A)
1. I click change target branches, go to that page and click Compare branches and continue
1. The description and title I filled in 4 are gone
# Possible solution:
Use the `autosave.js` plugin we already use when accidentaly closing the tab while editing/creating an issue/mr/comment
issue