Mount HDFS Dialog: basic support (#7580)

Implemented in this PR

- New base dialog for anything needing to work with the controller. This is important since going from SQL -> Controller we "should" have the right permissions but aren't guaranteed
- Support for Mount HDFS via a dialog. Includes basic polling for success/failure, but have to give up after 2.5min as mounting could take hours. By then it's assumed to be successful since server-side has 2min timeout built in.


Not implemented in this PR

- Script as Notebook button. This should convert the inputs to a set of cells in a notebook so users can run things themselves
- Updates based on PM / UX reviews. I think we'll need a round of feedback before completing this work.

extensions/big-data-cluster/src/bigDataCluster/constants.ts

@@ -72,3 +72,6 @@ export namespace cssStyles {
 }
 
 export type AuthType = 'integrated' | 'basic';
+
+export const clusterEndpointsProperty = 'clusterEndpoints';
+export const controllerEndpointName = 'controller';