feat: add API/SDK support for autostop extension (#1778)

* Adds deadline column to workspace_builds, associated DB/API plumbing
* database: Upon inserting a row into workspace_builds, deadline will 
  initially be zero.
* autobuild: Executor now checks the Deadline field of the workspace_build
  for the purpose of autostop logic.
* coderd: Adds a new route /api/v2/workspaces/:workspace/extend which allows
  updating the deadline of the currently active workspace build. The new
  deadline must be after the existing deadline, and not the zero time.
* provisionerd: updates workspace_build.deadline upon successful workspace 
  build completion (equal to now plus workspace TTL, if it exists).

coderd/database/queries/workspacebuilds.sql

@@ -101,16 +101,18 @@ INSERT INTO
 		transition,
 		initiator_id,
 		job_id,
-		provisioner_state
+		provisioner_state,
+		deadline
 	)
 VALUES
-	($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11) RETURNING *;
+	($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12) RETURNING *;
 
 -- name: UpdateWorkspaceBuildByID :exec
 UPDATE
 	workspace_builds
 SET
 	updated_at = $2,
-	provisioner_state = $3
+	provisioner_state = $3,
+	deadline = $4
 WHERE
 	id = $1;