s3, iam, volume, filer, master: add /healthz and /readyz health probes (#9738)

Adds standard Kubernetes liveness/readiness endpoints to all HTTP
servers that were missing them:

- S3:     adds /readyz (already had /healthz)
- IAM:    adds /healthz and /readyz (had none)
- Volume: adds /readyz (already had /healthz)
- Filer:  adds /readyz on default and readonly mux
- Master: adds /healthz and /readyz at root level
  (preserves existing /cluster/healthz)

All endpoints reuse existing health handlers or return 200 OK as a
minimal foundation. Future PRs can enhance /readyz with dependency
checks without breaking the contract.

Closes #9736

Co-authored-by: Mohamed Chorfa <mohamed.chorfa@thalesgroup.com>

weed/s3api/s3api_server.go

@@ -698,9 +698,10 @@ func (s3a *S3ApiServer) registerRouter(router *mux.Router) {
 	// plus REST-style endpoints for AWS CLI
 	s3a.registerS3TablesRoutes(apiRouter)
 
-	// Readiness Probe
+	// Health probes
 	apiRouter.Methods(http.MethodGet, http.MethodHead).Path("/status").HandlerFunc(s3a.StatusHandler)
 	apiRouter.Methods(http.MethodGet, http.MethodHead).Path("/healthz").HandlerFunc(s3a.StatusHandler)
+	apiRouter.Methods(http.MethodGet, http.MethodHead).Path("/readyz").HandlerFunc(s3a.StatusHandler)
 
 	// Object path pattern with (?s) flag to match newlines in object keys
 	const objectPath = "/{object:(?s).+}"