Improve API4 initialization (#18680)

* Improve API4 initialization

- Refactored openGraphDataCache to be inside app layer.
- Moved the cache instance from global variable to be inside server.
- Moved out the app instantiation from the global commands package
to be instantiated on every call. Only the server instance is passed.
- Moved InitLocal to be called from inside Init.

```release-note
NONE
```

* Remove commented line

```release-note
NONE
```

api4/openGraph.go

@@ -5,30 +5,13 @@ package api4
 
 import (
 	"net/http"
-	"time"
 
 	"github.com/mattermost/mattermost-server/v6/model"
-	"github.com/mattermost/mattermost-server/v6/services/cache"
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
-const OpenGraphMetadataCacheSize = 10000
-
-var openGraphDataCache = cache.NewLRU(cache.LRUOptions{
-	Size: OpenGraphMetadataCacheSize,
-})
-
 func (api *API) InitOpenGraph() {
 	api.BaseRoutes.OpenGraph.Handle("", api.APISessionRequired(getOpenGraphMetadata)).Methods("POST")
-
-	// Dump the image cache if the proxy settings have changed. (need switch URLs to the correct proxy)
-	api.app.AddConfigListener(func(before, after *model.Config) {
-		if (before.ImageProxySettings.Enable != after.ImageProxySettings.Enable) ||
-			(before.ImageProxySettings.ImageProxyType != after.ImageProxySettings.ImageProxyType) ||
-			(before.ImageProxySettings.RemoteImageProxyURL != after.ImageProxySettings.RemoteImageProxyURL) ||
-			(before.ImageProxySettings.RemoteImageProxyOptions != after.ImageProxySettings.RemoteImageProxyOptions) {
-			openGraphDataCache.Purge()
-		}
-	})
 }
 
 func getOpenGraphMetadata(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -46,20 +29,13 @@ func getOpenGraphMetadata(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	var ogJSONGeneric []byte
-	err := openGraphDataCache.Get(url, &ogJSONGeneric)
-	if err == nil {
-		w.Write(ogJSONGeneric)
-		return
-	}
-
-	og := c.App.GetOpenGraphMetadata(url)
-	ogJSON, err := og.ToJSON()
-	openGraphDataCache.SetWithExpiry(url, ogJSON, 1*time.Hour)
+	buf, err := c.App.GetOpenGraphMetadata(url)
 	if err != nil {
+		mlog.Warn("GetOpenGraphMetadata request failed",
+			mlog.String("requestURL", url),
+			mlog.Err(err))
 		w.Write([]byte(`{"url": ""}`))
 		return
 	}
-
-	w.Write(ogJSON)
+	w.Write(buf)
 }