Android-components: Allow specifying tokenserverUrl in ServerConfig

[grigoryk]

This is a follow-up to https://github.com/mozilla-mobile/android-components/pull/3579.

Currently, the only way to use a self-hosted sync server is by specifying a custom FxA endpoint via ServerConfig (which will then be used during tokenserver url configuration internally). However, self-hosting FxA server currently is not well documented, and generally quite experimental.

A much more common path - and this is what both Firefox Desktop and Firefox for Android currently support - is to specify a tokenserver URL. Token server in our current architecture is what's responsible for pointing the client to a specific storage node. In case of self-hosting, both a sync storage server and a token server are easily deployed via available docker containers.

By allowing specifying tokenserver url as part of the ServerConfig passed into the account manager, we're enabling easy use of self-hosted sync infrastructure.

Actual work here should be pretty trivial - making sure we override tokenserver url stored within the SyncAuthInfoCache.

[tublitzed]

I don't seem to have perms in this repo to assign this to myself, so just as a heads up; I'm currently working on this.

[Mugurell]

@tublitzed Are you still working on this? Do you need any help?

[tublitzed]

@Mugurell - thanks! Yes, I am. I wound up getting tasked with a lot of unrelated items, hence the delay here. Plan is get to a PR open here tomorrow then to come back and work on getting #3762 in Fenix connected to it.

[tublitzed]

This work is no longer going to happen in this repo. This first step will be handled here in app services and all the work is tracked here, in this epic

[eoger]

Can we close this? We have landed what's necessary in https://github.com/mozilla-mobile/fenix/pull/8916.

[kbrosnan]

Closing