Merge Request description template gets overriden by Jira issue link

Summary

If you have a default MR description template, but your branch name is following a pattern which Gitlab recognizes as 'a Jira issue', it will not use the template anymore but instead prefill the MR with 'Closes '. This breaks the template being a default, as people now need to manually select the template first. It breaks onboarding as well, with people needing to know there's a template first instead of it being prefilled automatically, bypassing the usefulness.

Steps to reproduce

  1. Have a default MR description template.
  2. Make a branch with a 'random name' and create an MR; this MR will prefill that template.
  3. Make a branch with a follows a Jira Issue naming pattern, (e.g. FE-1234-lalala), and create an MR; this MR will not prefill that template.

What is the current bug behavior?

It does not use the default MR template if you create an MR.

What is the expected correct behavior?

The default MR template should always be used.

Relevant logs and/or screenshots

Made a screen recording of this in action: create a branch and made an MR -> it uses the template. Create a branch with a specific name -> it does not use the template.

1080p

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info 
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check 
(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)


(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)


(we will only investigate if the tests are passing)

Possible fixes