chore: add support for one-way websockets to backend (#16853)

Closes https://github.com/coder/coder/issues/16775

## Changes made
- Added `OneWayWebSocket` function that establishes WebSocket
connections that don't allow client-to-server communication
- Added tests for the new function
- Updated API endpoints to make new WS-based endpoints, and mark
previous SSE-based endpoints as deprecated
- Updated existing SSE handlers to use the same core logic as the new WS
handlers

## Notes
- Frontend changes handled via #16855

coderd/coderd.go

@@ -1248,7 +1248,8 @@ func New(options *Options) *API {
 					httpmw.ExtractWorkspaceParam(options.Database),
 				)
 				r.Get("/", api.workspaceAgent)
-				r.Get("/watch-metadata", api.watchWorkspaceAgentMetadata)
+				r.Get("/watch-metadata", api.watchWorkspaceAgentMetadataSSE)
+				r.Get("/watch-metadata-ws", api.watchWorkspaceAgentMetadataWS)
 				r.Get("/startup-logs", api.workspaceAgentLogsDeprecated)
 				r.Get("/logs", api.workspaceAgentLogs)
 				r.Get("/listening-ports", api.workspaceAgentListeningPorts)
@@ -1280,7 +1281,8 @@ func New(options *Options) *API {
 				r.Route("/ttl", func(r chi.Router) {
 					r.Put("/", api.putWorkspaceTTL)
 				})
-				r.Get("/watch", api.watchWorkspace)
+				r.Get("/watch", api.watchWorkspaceSSE)
+				r.Get("/watch-ws", api.watchWorkspaceWS)
 				r.Put("/extend", api.putExtendWorkspace)
 				r.Post("/usage", api.postWorkspaceUsage)
 				r.Put("/dormant", api.putWorkspaceDormant)