[dagit] Fix cache reading in Schedules/Sensors section
Now that the left nav allows multiple repositories to be selected, the Schedules/Sensors section does not update status correctly. This is because the queries are manually performed in an array of client.query calls, and do not subscribe to the cache.
Repair this by switching to watchQuery subscriptions, which will observe the cache. When data arrives, update interal state of JobsList.
Test Plan: Run dagit, switch schedules and sensors on and off. Verify that the status dot is shown or hidden accordingly.
Reviewers: dgibson, bengotow, prha
Reviewed By: dgibson
Differential Revision: https://dagster.phacility.com/D7220