Use embedded version of Element Call (#4470)

* Use embedded version of Element Call: for in-app room calls, the app will use an embedded version of Element Call shipped with the app instead of using an external service.

* Remove `ElementCallBaseUrlProvider` so we don't use the Element well known file to get the base URL anymore

* Remove `ElementCallConfig.DEFAULT_BASE_URL` since it's not used anymore

* Restore the usage of the custom EC base URL in developer settings as the actual base URL, it present

* Add a way to customise the embedded EC analytic credentials

* Update CI to use the EC analytic credentials as secrets

* Improve the custom URL placeholder to include the `/room` suffix

appconfig/src/main/kotlin/io/element/android/appconfig/ElementCallConfig.kt

@@ -8,11 +8,6 @@
 package io.element.android.appconfig
 
 object ElementCallConfig {
-    /**
-     * The default base URL for the Element Call service.
-     */
-    const val DEFAULT_BASE_URL = "https://call.element.io"
-
     /**
      * The default duration of a ringing call in seconds before it's automatically dismissed.
      */