Unique observer submenus for non-standard marine squads

[Steelpoint]

About the pull request

This PR adds sub-menus for most non-standard marine squads. This includes SOF (Marine Raiders), CBRN, Echo Squad, and Forecon (ERT only, not survivors). This also changes the colour of Foxtrot from Teal to a similar brownish colour.

Explain why it's good for the game

Better tracking of non-standard squads for when they appear.

Testing Photographs and Procedure

Changelog

🆑
add: Marine Special Forces, Forecon, Echo Squad and CBRN will now appear in their own sub-menu for observers.
ui: Foxtrot's colour in the observe menu now reflects the squads true colour scheme.
/:cl:

[Steelpoint]

I was torn regarding adding Intel Officers as a separate squad, I decided against it, to avoid cluttering the squad menu at round start, unless a request is made to add them as well.

[github-actions]

This PR has been inactive for long enough to be automatically marked as stale. This means it is at risk of being auto closed in ~ 7 days, please address any outstanding review items and ensure your PR is finished, if these are all true and you are auto-staled anyway, you need to actively ask maintainers if your PR will be merged. Once you have done any of the previous actions then you should request a maintainer remove the stale label on your PR, to reset the stale timer. If you feel no maintainer will respond in that time, you may wish to close this PR youself, while you seek maintainer comment, as you will then be able to reopen the PR yourself