android: make Maven repo used for publising configurable

android/build.gradle

         publishing {
             publications {}
             repositories {
-                maven { url "file:${rootProject.projectDir}/../../jitsi-maven-repository/releases" }
+                maven { url "file:${rootProject.ext.mavenRepo}" }
             }
         }
     }
     // of ours.
     moduleGroupId = 'com.facebook.react'
 
+    // Maven repo where artifacts will be published
+    mavenRepo = System.env.MVN_REPO ?: "${rootProject.projectDir}/../../jitsi-maven-repository/releases"
+
     // Glide
     excludeAppGlideModule = true
     glideVersion = "4.7.1"  // keep in sync with react-native-fast-image

android/sdk/build.gradle

 
     }
     repositories {
-        maven { url "file:${rootProject.projectDir}/../../jitsi-maven-repository/releases" }
+        maven { url "file:${rootProject.ext.mavenRepo}" }
     }
 }