Azure: add PostgresSQL support and refactor to use resource graph (#8046)

* Azure: add PostgresSQL support and refactor to use resource graph
- Refactored to use @azure/arm-resourcegraph for all queries
- Refactored database lookup to do just 2 queries
(all servers, all DBS) instead of waiting serially on 1 query per RG
- Added Azure Database for PostgresSQL Servers support in the tree
- Removed use of older azure APIs in preference to ones compatible with resource graph
- Note: Had to use v1.0 of new subscriptions package because resourcegraph is 2month out of date vs all other packages

extensions/azurecore/extension.webpack.config.js

@@ -15,7 +15,8 @@ module.exports = withDefaults({
 		extension: './src/extension.ts'
 	},
 	externals: {
-		'ms-rest': 'commonjs ms-rest',
+		'@azure/ms-rest-azure-js': 'commonjs @azure/ms-rest-azure-js',
+		'@azure/ms-rest-js': 'commonjs @azure/ms-rest-js',
 		'request': 'commonjs request'
 	}
 });