docs: add synopsis to fork, opentofu, and auth docker commands

Brendan Lynchrequested to merge
8263-add-fork-opentofu-docker-synopsis into main

What does this MR do and why?

Adds Long (Synopsis) fields to five commands that were missing them, as part of the style guide audit identified in #8263 (closed).

Commands updated:

  • repo fork
  • opentofu init
  • opentofu state download
  • opentofu state delete
  • auth configure-docker

Content follows the documentation style guide and the GitLab CLI (glab) documentation style guide.

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