feat: use agent v2 API to fetch manifest (#11832)

Agent uses the v2 API to obtain the manifest, instead of the HTTP API.

coderd/agentapi/api.go

@@ -97,6 +97,16 @@ func New(opts Options) *API {
 		AgentFn:                  api.agent,
 		Database:                 opts.Database,
 		DerpMapFn:                opts.DerpMapFn,
+		WorkspaceIDFn: func(ctx context.Context, wa *database.WorkspaceAgent) (uuid.UUID, error) {
+			if opts.WorkspaceID != uuid.Nil {
+				return opts.WorkspaceID, nil
+			}
+			ws, err := opts.Database.GetWorkspaceByAgentID(ctx, wa.ID)
+			if err != nil {
+				return uuid.Nil, err
+			}
+			return ws.Workspace.ID, nil
+		},
 	}
 
 	api.ServiceBannerAPI = &ServiceBannerAPI{