Remove Issue Data and Actions docs page

Necessary steps

1. Identify parts of it that are not documented anywhere else and move them elsewhere:
   • Reference - make into a task topic and add to https://gitlab.com/gitlab-org/gitlab/blob/master/doc/user/project/issues/managing_issues.md
   • Email - make into a task topic and add to https://gitlab.com/gitlab-org/gitlab/blob/master/doc/user/project/issues/managing_issues.md
   • Mentions - move to https://gitlab.com/gitlab-org/gitlab/blob/master/doc/user/discussions/index.md
   • Award emoji is covered in https://docs.gitlab.com/ee/user/award_emojis.html, but add to the latter the mention of:

     ...from the list of available GitLab Flavored Markdown emojis.

   • Create merge request - mention in https://gitlab.com/gitlab-org/gitlab/blob/master/doc/user/project/merge_requests/getting_started.md#user-content-merge-requests-to-close-issues
   • Activity sort order move to https://gitlab.com/gitlab-org/gitlab/blob/master/doc/user/discussions/index.md
   • Publish an issue move to https://gitlab.com/gitlab-org/gitlab/blob/master/doc/user/project/issues/managing_issues.md
2. Delete the issue_data_and_actions.md page and also:
   • Set a redirect to https://docs.gitlab.com/ee/user/project/issues/
   • Delete images in https://gitlab.com/gitlab-org/gitlab/blob/master/doc/user/project/issues/img that are only linked from the Data and Actions page.
3. 🎉 🥂

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Original description

Problem

As pointed out by @sstern, the docs page at https://docs.gitlab.com/ee/user/project/issues/issue_data_and_actions.html is out of date with a pretty old screenshot. We should update this page or replace it with a new page that's easier to maintain.

Proposal

This page will go out of date pretty quickly as we iterate on issues. Some ideas:

• Look at how often this page is actually used. If it gets no traffic, remove it.
• Break up the page into separate pages for the issue body/description, comment area, and issue sidebar. Have separate screenshots for each. Individual screenshots will probably go out of date at a slower rate than a single screenshot for the whole thing.