added checks for audience and issuer values (#1772)
added checks for audience and issuer values (#1772)

* added checks for audience and issuer values
default audience and issuer checks to validate only appId
added missing documentation lines from the previous PR for context_user and context_group session values

* support for accepting any audience
option set to accept any audience by default

jitsi/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,bgrozev/jitsi-meet,bgrozev/jitsi-meet,bgrozev/jitsi-meet,gpolitis/jitsi-meet,bgrozev/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,bgrozev/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,bgrozev/jitsi-meet