Bug 1823462 - New application-services release system

Application services is going to switch to rapid-release / train style
model where:
  - The version numbers correspond to the Fx version (113.x for the
    current nightly cycle).
  - There are nightly builds for the current nightly release (for
    example 113.[timestamp]
  - At the end of the nightly release cycle, there's a release (for
    example 113.0)
  - There may be subsequent releases if changes are uplifted (for
    example 113.1)

- Updated the gradle code to handle the new system.  The application
  services versioning is stored in the version/channel fields of the
  `ApplicationServicesConfig` object.
- Updated the gradle code to fetch packages from the Maven
  nightly/staging repos if needed.
- Updated relbot to 6.1.0.  This is needed to handle the a-s nightly
  version bump.
- Updated creating-a-release-branch docs

mobile/android/android-components/build.gradle

@@ -63,6 +63,13 @@ allprojects {
             name "Mozilla"
             url "https://maven.mozilla.org/maven2"
         }
+
+        if (ExtraRepositories.mozillaStaging) {
+            maven {
+                name "Mozilla Staging"
+                url "https://maven-default.stage.mozaws.net/maven2"
+            }
+        }
     }
 }