chore: update .dockerignore to include android directory and add android/.gitignore for build artifacts

.dockerignore

@@ -8,6 +8,7 @@ docs/
 # Development files
 .github/
 electron/
+android/
 scripts/
 Makefile
 

android/.gitignore

@@ -0,0 +1,16 @@
+*.iml
+.gradle
+/local.properties
+/.idea/caches
+/.idea/libraries
+/.idea/modules.xml
+/.idea/workspace.xml
+/.idea/navEditor.xml
+/.idea/assetWizardSettings.xml
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+local.properties
+