feat(inIframe/isEmbedded) add ability to detect generic embedding

[saghul]

On web we detect if we run on an iframe, and on mobile we detect if the app is one of ours.

[damencho]

LGTM, but let's wait and for @hristoterezov :)

[hristoterezov]

I still like the alternative approach better where we allow to override the options for all RN use cases and then have a whitelist in the JitsiMeet App for the things we care about from the apps perspective. In practice this is the same thing and we just have exception for the JitsiMeet App but for any other RN app that uses the SDK those will be allowed and it will be apps responsibility to not pass unverified values for these props. So I don't see much value in the exception for our app...

But this is personal preference and I'd say even this approach is acceptable although I like more the other one.

Added some questions and comments. I think we can definitely reduce the list of the allowed config props.

[saghul]

@hristoterezov PTAL. It now includes the timeout implementation for mobile.

[saghul]

Jenkins please test this please.

[hristoterezov]

I think this array needs to be empty!

[saghul]

@damencho Tests passed but the CI choked on something regarding my branch:

Switched to a new branch 'is-embedded'
+ git pull https://github.com/saghul/jitsi-meet.git is-embedded
From https://github.com/saghul/jitsi-meet
 * branch                is-embedded -> FETCH_HEAD
fatal: It seems that there is already a rebase-merge directory, and
I wonder if you are in the middle of another rebase.  If that is the
case, please try
	git rebase (--continue | --abort | --skip)
If that is not the case, please
	rm -fr ".git/rebase-merge"
and run me again.  I am stopping in case you still have something
valuable there.

Build step 'Execute shell' marked build as failure