[1.x] videoroom: support of string_ids/string_ids_user

[IgorKhomenko]

This is more a feature request rather than an issue.

There is a case when integrate Janus with 3rd party system where room id is a string, but user id is a number.

With current version of Janus, it's only possible to have ether string or number for both.

It would be very useful to have a way to configure it separately, e.g. to set string_ids = TRUE; and to have a separate variable for users: string_ids_user = FALSE;
https://github.com/meetecho/janus-gateway/blob/master/src/plugins/janus_videoroom.c#L1951

I already have a custom branch with this change and wondering is it something you are interested in to have, so I could do a PR.

Thank you in advance

[amnonbb]

In our case we need change for users string but leave rooms with number. Is it possible in your branch?

[IgorKhomenko]

@amnonbb here is a PR #3369