Details about sphinx-terminal

[msuchane]

Some useful options for the sphinx-terminal extension were missing. I've added one (:dir:) and linked the upstream documentation for the rest.

[minaelee]

Failing linkcheck tests due to malformed URLs, see suggestions. Ty!

[minaelee]

Requesting review from @jahn-junior also because he has been working on terminal extension updates recently, maybe there's something to be noted here.

[jahn-junior]

Thanks for doing this! I've found that a handful of the terminal directive's options are unknown to most of the team. It looks like you've got a good handle on this, but feel free to reach out if you have any questions. 👍

[msuchane]

I think this should now be ready to merge. I've applied all suggestions.

[jahn-junior]

Thanks!

[minaelee]

Thanks Marek!

In general, I think we need to flag all custom Canonical Sphinx directives as such (explicitly mentioning they are not a part of MyST or rST standard syntax), including any information about versions and options (such as the copy option), but this can be a part of the starter pack docs updates epic next cycle rather than holding up this PR.