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/databasefake/databasefake.go

@@ -1485,6 +1485,7 @@ func (q *fakeQuerier) InsertWorkspaceBuild(_ context.Context, arg database.Inser
 		InitiatorID:       arg.InitiatorID,
 		JobID:             arg.JobID,
 		ProvisionerState:  arg.ProvisionerState,
+		Deadline:          arg.Deadline,
 	}
 	q.workspaceBuilds = append(q.workspaceBuilds, workspaceBuild)
 	return workspaceBuild, nil
@@ -1693,6 +1694,7 @@ func (q *fakeQuerier) UpdateWorkspaceBuildByID(_ context.Context, arg database.U
 		}
 		workspaceBuild.UpdatedAt = arg.UpdatedAt
 		workspaceBuild.ProvisionerState = arg.ProvisionerState
+		workspaceBuild.Deadline = arg.Deadline
 		q.workspaceBuilds[index] = workspaceBuild
 		return nil
 	}