Add code sharing sample (#1444)

* code-sharing boilerplate

* initial commit of code-sharing logic

* documentation improvements

* added code-sharing to samples.yaml

* Updated counter UI to visually indicate communication with the server

* added code_sharing to CI

* CI changes to code_sharing

* fixed test with DI

* formatting

* added shared module to CI

* adds forgotten CI change

code_sharing/client/.metadata

@@ -0,0 +1,45 @@
+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled.
+
+version:
+  revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+  channel: main
+
+project_type: app
+
+# Tracks metadata for the flutter migrate command
+migration:
+  platforms:
+    - platform: root
+      create_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+      base_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+    - platform: android
+      create_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+      base_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+    - platform: ios
+      create_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+      base_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+    - platform: linux
+      create_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+      base_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+    - platform: macos
+      create_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+      base_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+    - platform: web
+      create_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+      base_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+    - platform: windows
+      create_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+      base_revision: f16fe11ecf81a85d926ea3817ba1c87bdbbefa41
+
+  # User provided section
+
+  # List of Local paths (relative to this file) that should be
+  # ignored by the migrate tool.
+  #
+  # Files that are not part of the templates will be ignored by default.
+  unmanaged_files:
+    - 'lib/main.dart'
+    - 'ios/Runner.xcodeproj/project.pbxproj'