Add ICS route for each sub-team

[afragen]

I know there's a route to download an ICS file for a specific team meetings-$team.ics, like all of the core teams, but for those who only want a single team like meetings-core-dev.ics or meetings-core-meta.ics, etc. there must be a better way.

It might be that also filtering within the core team, etc. might be a better path.

[tellyworth]

Perhaps we could add routes for filtering based on the Slack channel. Like meetings.ics?location=core-dev or similar.

[afragen]

Whichever method can provide an ICS file with only those data from an individual meeting group would be great!