feat(web): make api.keyman.com endpoint configurable

> Is there any way to setup KeymanWeb to query a local api.keyman.com.localhost endpoint and reference a local s.keyman.com.localhost, e.g. when testing on help.keyman.com.localhost/keyboard? Currently it seems like the api reference is hardcoded:

https://github.com/keymanapp/keyman/blob/0288048340864e988121e39c0ef23e321067ac76/web/src/engine/keyboard-storage/src/cloud/queryEngine.ts#L108-L109

@jahorton writes:

> We could design a new config parameter to be passed in.
> https://github.com/keymanapp/keyman/blob/0288048340864e988121e39c0ef23e321067ac76/web/src/engine/keyboard-storage/src/cloud/queryEngine.ts#L68
> `pathConfig` comes from the engine configuration built during engine init, so we already have a way to pass parameters in.