Add metrics for total number of active workspaces

MR: Add metric for active workspaces (!191902 - merged)

Description

Add metrics for active workspace, including both new and existing workspaces combined.

We will use internal event tracking with additional properties to distinguish new and existing workspaces.

The place we trigger events would be at workspace model ee/app/models/remote_development/workspace.rb, and we use after_save hook to inject event trigger. We should make sure even if this tracking method goes wrong, then overall operation still goes well (use rescue block).

For metrics, we should have 1 metric for whole event, and 2 separate metric each for started and restarted.

IF `desired_state` changed to `Running`? THEN
  IF another `desired_state` changed to `Running` after last `desired_state` changed to `Running`
    SKIP
  ELSE IF new record
    THEN track event with `new`
  ELSE
    THEN track event with `existing`

Acceptance criteria

• Define 1 internal event for active workspaces
• Trigger each event using after_save in workspace model (See pseudo code for reference)
• Define 3 service ping metrics for all, new and existing
• Ensure all metrics as expected in Tableau

Implementation plan

NA