Notification setting for invites

[pixlwave]

Add a setting with a toggle in the notifications setting screen to enable / disable the notification for invites, in the Additional settings section which has to be unhidden (currently hidden, since it only contains call setting which is hidden - the call settings stay hidden), with the wording Invitations, and enabled by default (note that we read the value from the SDK, and it should be true by default, that's the default push rules).

Using matrix-org/matrix-rust-sdk#2908. Android reference element-hq/element-x-android#1955