add room header when externals are allowed

[odelcroi]

With the header :

Test :

• 1 : create a room with external allowed, check that the header is displayed
• 2 : create a private room without external allowed, check that the header is NOT displayed
• 3 : create a private room, after the creation, allow external in the settings, check that the header is displayed

e2e :

• 1 : create a room with external allowed, check that the header is displayed
• 2 : create a private room without external allowed, check that the header is NOT displayed

UI :

• : check responsiveness -> N/A

[estellecomment]

je mettrais bien cette fonction dans TchapRoomUtils

[odelcroi]

si tu veux :)

[estellecomment]

cypress is broken locally and in CI, but I can't figure out why. Later.