Add features option in JWT payload

[kassle]

Some features in jitsi-meet is configurable from JWT payload. one of them is the "screen-sharing" which is very important, and jitsi-meet will disable the screen-sharing when not configured in JWT payload.

https://community.jitsi.org/t/how-can-i-enable-shared-screen-for-moderators-using-jwt/83834/3

it would be nice if this beloved plugin support adding features in JWT payload