Activate audio and video call based on featureflag

[odelcroi]

See config files :
https://github.com/tchapgouv/tchap-web-v4/blob/e1b718e098fde7ea48a76384c7ab7984686f1a44/config.dev.json

With External users before :

With External users after :

With Audio call before :

With Audio call after :

Checklist

[odelcroi]

@areox-net the caption "ouvert aux externes" was easier to set before the name of the room, do you see a problem?

[areox-net]

@odelcroi It's not the best solution, but I understand it's better for rooms with long titles.
Ideally, I'd put it under the room name in a Title+Subtitle logic.

[NicolasBuquet]

@odelcroi : Shouldn't we leave video call out of scope in this PR?

[odelcroi]

@odelcroi It's not the best solution, but I understand it's better for rooms with long titles. Ideally, I'd put it under the room name in a Title+Subtitle logic.

In this new version, under the room title, there is the room descritpion

[odelcroi]

@odelcroi : Shouldn't we leave video call out of scope in this PR?

The video button is hidden with a feature flag, then we can display it progressively with no code modification