Add config option to filter out calls from creating new rooms

[illgitthat]

Currently, every time you receive a call a new matrix room is created.

Potentially relevant code: https://github.com/mautrix/gvoice/blob/main/pkg/libgv/gvproto/threads.pb.go#L32

ThreadFolder_ALL_CALL_THREADS

[Fmstrat]

Agreed, my server is flooded with rooms now. Would be better if all calls from an individual showed up in the same room as SMS.

[clari7744]

agreed with fmstrat; i'd like it to show up as "call" in the SMS thread - if it's possible to include elapsed time as well that'd be cool otherwise just having it show up as a call and ending it there rather than starting a new room