Migrate empty manifest package attribute to namespace DSL (duckduckgo#2133)

Task/Issue URL: https://app.asana.com/0/488551667048375/1202710479869541/f

### Description
AGP will not allow setting the package attribute in the source AndroidManifest.xml starting in AGP 8.0. Instead, users must specify a namespace via the namespace DSL.

This PR migrates our empty manifest to use `namespace` DSL

### Steps to test this PR
- [x] app builds
- [x] smoke test for app and AppTP

Author: aitorvs

anrs/anrs-api/build.gradle

@@ -26,3 +26,7 @@ dependencies {
     implementation AndroidX.core.ktx
     implementation KotlinX.coroutines.core
 }
+
+android {
+  namespace 'com.duckduckgo.anrs.api'
+}

anrs/anrs-api/src/main/AndroidManifest.xml

@@ -47,4 +47,5 @@ android {
     anvil {
         generateDaggerFactories = true // default is false
     }
+  namespace 'com.duckduckgo.app.anr'
 }

anrs/anrs-impl/build.gradle

@@ -50,3 +50,7 @@ dependencies {
     testImplementation project(path: ':common-test')
 }
 
+
+android {
+  namespace 'com.duckduckgo.app.anrs.store'
+}

anrs/anrs-impl/src/main/AndroidManifest.xml

@@ -32,4 +32,7 @@ dependencies {
     implementation "com.jakewharton.threetenabp:threetenabp:_"
 
     kapt AndroidX.room.compiler
-}
+}
+android {
+  namespace 'com.duckduckgo.app'
+}

anrs/anrs-store/build.gradle

@@ -29,3 +29,7 @@ dependencies {
     implementation AndroidX.constraintLayout
 }
 
+
+android {
+  namespace 'com.duckduckgo.autofill.api'
+}