Notebooks: Fix strict compile errors (#12591)

* strict compile for sqlSessionManager.ts

* start clientSession.ts fixes

* strict compile for clientSession.ts

* strict compile for notebookModel.ts

* add display name

* clean up code

* clean up code

* initialize string to empty string

* address PR comments

* address PR comments

* address PR comments

* remove errorMessage check

extensions/notebook/src/test/model/sessionManager.test.ts

@@ -186,7 +186,8 @@ describe('Jupyter Session', function (): void {
 
 		// When I call changeKernel on the wrapper
 		let kernel = await session.changeKernel({
-			name: 'python'
+			name: 'python',
+			display_name: 'Python'
 		});
 		// Then I expect it to have the ID, and only be called once
 		should(kernel.id).equal('id');