use internalImplementation for sync related modules (duckduckgo#2877)

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Task/Issue URL:
https://app.asana.com/0/488551667048375/1204020855860985/f

### Description
This configures sync related modules to be built for internal flavor
only.

### Steps to test this PR

_Build internal_
- [ ] smoke test sync

Author: karlenDimla

app/build.gradle

@@ -247,10 +247,10 @@ dependencies {
     implementation project(':element-hiding-impl')
     implementation project(':element-hiding-store')
 
-    implementation project(':sync-api')
-    implementation project(':sync-impl')
-    implementation project(':sync-store')
-    implementation project(':sync-lib')
+    internalImplementation project(':sync-api')
+    internalImplementation project(':sync-impl')
+    internalImplementation project(':sync-store')
+    internalImplementation project(':sync-lib')
 
     implementation project(':request-filterer-api')
     implementation project(':request-filterer-impl')