Medical - Add `ace_medical_enabled` variable for future-proofing API

[LinkIsGrim]

When merged this pull request will:

• Add a variable for 3rd party to check against for medical's overall enabled status. Hard set here, switch to setting when we implement it.

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[johnb432]

I'm a bit confused as to why you want to add this now, especially as atm it's not looking bright for #9593. I'm just not sure if it will ever be a setting, given that the requests we've made to BI to make it work as a setting have been ignored.

[jonpas]

Definitely not 3.17.1.

[LinkIsGrim]

Should followup by making everything else check for this as well.