Add explicit SDK version to messaging AAR. (#1523)

* Add SDK version to messaging AAR. * Add readme. * Switch minSdkVersion to 14.

Author: jonsimantov

messaging/messaging_java/build.gradle

@@ -43,6 +43,10 @@ android {
  }
  compileSdkVersion 33
 
+ defaultConfig {
+ minSdkVersion 14
+ }
+
  sourceSets {
  main {
  manifest.srcFile '../src/android/java/LibraryManifest.xml'

release_build_files/readme.md

@@ -636,6 +636,8 @@ code.
  - Dynamic Links: The Dynamic Links SDK is now deprecated. See the [support
  documentation](https://firebase.google.com/support/dynamic-links-faq)
  for more information.
+ - Messaging (Android): Fixed minSdkVersion in the firebase_messaging.aar
+ manifest file.
 
 ### 11.7.0
 - Changes