Merge pull request #50550 from atlassian/cleanup-configz

Automatic merge from submit-queue (batch tested with PRs 50550, 50768)

Cleanup locking in configz

**What this PR does / why we need it**:
- Reduce scope of lock in `write()` method
- Use the read lock in `write()` method

**Release note**:
```release-note
NONE
```
/kind cleanup

@mikedanese 

p.s. looks like the `Set()` method could be removed if the value is accepted as an argument to `New()`. I.e. looks like to code re-sets the value.

pkg/util/configz/configz.go

@@ -75,9 +75,13 @@ func handle(w http.ResponseWriter, r *http.Request) {
 }
 
 func write(w io.Writer) error {
-	configsGuard.Lock()
-	defer configsGuard.Unlock()
-	b, err := json.Marshal(configs)
+	var b []byte
+	var err error
+	func() {
+		configsGuard.RLock()
+		defer configsGuard.RUnlock()
+		b, err = json.Marshal(configs)
+	}()
 	if err != nil {
 		return fmt.Errorf("error marshaling json: %v", err)
 	}