Add documentation for boards epic create

Merged Kushal Pandya requested to merge docs-boards-epic-create into master

What does this MR do?

Add missing documentation for epic create from boards, as introduced in !63999 (merged).

Feature issue: #233568 (closed)

Related issues

Author's checklist

To avoid having this MR be added to code verification QA issues, don't add these labels: feature, frontend, backend, ~"bug", or database

Review checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

  • If the content requires it, ensure the information is reviewed by a subject matter expert.
  • Technical writer review items:
    • Ensure docs metadata is present and up-to-date.
    • Ensure the appropriate labels are added to this MR.
    • If relevant to this MR, ensure content topic type principles are in use, including:
      • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
      • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
      • Any task steps should be written as a numbered list.
      • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
  • Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
  • Ensure a release milestone is set.
Edited by Marcin Sedlak-Jakubowski