Implement the service ping for workspaces actions

See &10123 for details.

Add metrics for:

1. How many unique monthly active users interacted with a workspace (create, open, terminate)
2. The number of agents configured to support remote development
3. The number of workspaces associated with a project (as in, gitlab-org had 240 workspaces created last month)

To be handled in a another issue:

1. The average length of time a workspace is running
2. The total number of workspaces started in a month (not just created, but eventually "resumed")