Add Chrome store policy compliant names/descriptions (#13142)

The Chrome Web Store has spam policies that prevent uploading
extensions that are too similar to each other. There are exceptions for
test and development versions of extensions, but these exceptions are
required to be clearly identified in the name and description of the
extension.

The name and description of both the Flask and beta distributions have
been updated to include explicit all-caps declarations that identify
them as development and beta distributions respectively, in-line with
the examples shown in the Chrome Web Store spam FAQ.

For more information, see: https://developer.chrome.com/docs/webstore/spam-faq/#test-version

app/build-types/beta/manifest/chrome.json

@@ -0,0 +1,4 @@
+{
+  "description": "THIS IS THE METAMASK EXTENSION BETA, INTENDED FOR BETA TESTING",
+  "name": "MetaMask BETA"
+}

app/build-types/flask/manifest/chrome.json

@@ -0,0 +1,4 @@
+{
+  "description": "THIS IS THE CANARY DISTRIBUTION OF THE METAMASK EXTENSION, INTENDED FOR DEVELOPERS.",
+  "name": "MetaMask Flask DEVELOPMENT BUILD"
+}