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
```

app/opengraph.go

@@ -7,6 +7,7 @@ import (
 	"html"
 	"io"
 	"net/url"
+	"time"
 
 	"github.com/dyatlov/go-opengraph/opengraph"
 	"golang.org/x/net/html/charset"
@@ -14,16 +15,36 @@ import (
 	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
-const MaxOpenGraphResponseSize = 1024 * 1024 * 50
+const (
+	MaxOpenGraphResponseSize   = 1024 * 1024 * 50
+	openGraphMetadataCacheSize = 10000
+)
+
+func (a *App) GetOpenGraphMetadata(requestURL string) ([]byte, error) {
+	var ogJSONGeneric []byte
+	err := a.Srv().openGraphDataCache.Get(requestURL, &ogJSONGeneric)
+	if err == nil {
+		return ogJSONGeneric, nil
+	}
 
-func (a *App) GetOpenGraphMetadata(requestURL string) *opengraph.OpenGraph {
 	res, err := a.HTTPService().MakeClient(false).Get(requestURL)
 	if err != nil {
-		mlog.Debug("GetOpenGraphMetadata request failed", mlog.String("requestURL", requestURL), mlog.Err(err))
-		return nil
+		return nil, err
 	}
 	defer res.Body.Close()
-	return a.parseOpenGraphMetadata(requestURL, res.Body, res.Header.Get("Content-Type"))
+
+	graph := a.parseOpenGraphMetadata(requestURL, res.Body, res.Header.Get("Content-Type"))
+
+	ogJSON, err := graph.ToJSON()
+	if err != nil {
+		return nil, err
+	}
+	err = a.Srv().openGraphDataCache.SetWithExpiry(requestURL, ogJSON, 1*time.Hour)
+	if err != nil {
+		return nil, err
+	}
+
+	return ogJSON, nil
 }
 
 func (a *App) parseOpenGraphMetadata(requestURL string, body io.Reader, contentType string) *opengraph.OpenGraph {