fix: coderd: decouple ttl and deadline (#2282)

This commit makes the following changes:

- Partially reverts the changes of feat: update workspace deadline when workspace ttl updated #2165, making the deadline of a running workspace build independant of TTL, once started.
- CLI: updating a workspace TTL no longer updates the deadline of the workspace.
- UI: updating a workspace TTL no longer updates the deadline of the workspace.
- Drive-by: API: When creating a workspace, default TTL to min(12 hours, template max_ttl) if not instructed otherwise.
- Drive-by: CLI: list: measure workspace extension correctly (+X in last column) from the time the provisioner job was completed
- Drive-by: WorkspaceSchedule: show timezone of schedule if it is set, defaulting to dayjs guess otherwise.
- Drive-by: WorkspaceScheduleForm: fixed an issue where deleting the "TTL" value in the form would show the text "Your workspace will shut down a few seconds after start".

cli/list.go

@@ -127,6 +127,9 @@ func hasExtension(ws codersdk.Workspace) (bool, time.Duration) {
 	if ws.LatestBuild.Transition != codersdk.WorkspaceTransitionStart {
 		return false, 0
 	}
+	if ws.LatestBuild.Job.CompletedAt == nil {
+		return false, 0
+	}
 	if ws.LatestBuild.Deadline.IsZero() {
 		return false, 0
 	}
@@ -134,7 +137,7 @@ func hasExtension(ws codersdk.Workspace) (bool, time.Duration) {
 		return false, 0
 	}
 	ttl := time.Duration(*ws.TTLMillis) * time.Millisecond
-	delta := ws.LatestBuild.Deadline.Add(-ttl).Sub(ws.LatestBuild.CreatedAt)
+	delta := ws.LatestBuild.Deadline.Add(-ttl).Sub(*ws.LatestBuild.Job.CompletedAt)
 	if delta < time.Minute {
 		return false, 0
 	}