MM-49984: Displaying active search backend in system console (#22721)

This will be shown in the system console to let users know
which search backend is active.

Implemented via adding an extra param in the ping response.

https://mattermost.atlassian.net/browse/MM-49984

```release-note
The database section in the system console now has an additional
read-only section which shows the active search backend in use.

This can be helpful to confirm which is the currently active
search engine when there are multiple of them configured.
```
---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/platform/services/searchengine/searchengine.go

@@ -45,8 +45,19 @@ func (seb *Broker) GetActiveEngines() []SearchEngineInterface {
 	if seb.ElasticsearchEngine != nil && seb.ElasticsearchEngine.IsActive() {
 		engines = append(engines, seb.ElasticsearchEngine)
 	}
-	if seb.BleveEngine != nil && seb.BleveEngine.IsActive() {
+	if seb.BleveEngine != nil && seb.BleveEngine.IsActive() && seb.BleveEngine.IsIndexingEnabled() {
 		engines = append(engines, seb.BleveEngine)
 	}
 	return engines
 }
+
+func (seb *Broker) ActiveEngine() string {
+	activeEngines := seb.GetActiveEngines()
+	if len(activeEngines) > 0 {
+		return activeEngines[0].GetName()
+	}
+	if *seb.cfg.SqlSettings.DisableDatabaseSearch {
+		return "none"
+	}
+	return "database"
+}