MM-22051: Remove ToJson methods from network writes (#17999)

We replace the double conversion of
[]byte to string, with a direct write
to http.ResponseWriter.

https://mattermost.atlassian.net/browse/MM-22051

Tried using gofmt -r, but it only accepts Go
expressions. So had to resort to an ugly sed replace

sed -E -i 's/w.Write\(\[\]byte\((.*).ToJson\(\)\)\)/if err := json.NewEncoder\(w\).Encode\(\1\); err != nil { mlog.Warn\("Error while writing response", mlog.Err\(err\)\)}/g' *.go

```release-note
NONE
```

api4/plugin.go

@@ -162,7 +162,9 @@ func installMarketplacePlugin(c *Context, w http.ResponseWriter, r *http.Request
 	auditRec.AddMeta("plugin_desc", manifest.Description)
 
 	w.WriteHeader(http.StatusCreated)
-	w.Write([]byte(manifest.ToJson()))
+	if err := json.NewEncoder(w).Encode(manifest); err != nil {
+		mlog.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 func getPlugins(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -182,7 +184,9 @@ func getPlugins(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	w.Write([]byte(response.ToJson()))
+	if err := json.NewEncoder(w).Encode(response); err != nil {
+		mlog.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 func getPluginStatuses(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -202,7 +206,9 @@ func getPluginStatuses(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	w.Write([]byte(response.ToJson()))
+	if err := json.NewEncoder(w).Encode(response); err != nil {
+		mlog.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 func removePlugin(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -386,7 +392,9 @@ func installPlugin(c *Context, w http.ResponseWriter, plugin io.ReadSeeker, forc
 		return
 	}
 	w.WriteHeader(http.StatusCreated)
-	w.Write([]byte(manifest.ToJson()))
+	if err := json.NewEncoder(w).Encode(manifest); err != nil {
+		mlog.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 func setFirstAdminVisitMarketplaceStatus(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -444,5 +452,7 @@ func getFirstAdminVisitMarketplaceStatus(c *Context, w http.ResponseWriter, r *h
 	}
 
 	auditRec.Success()
-	w.Write([]byte(firstAdminVisitMarketplaceObj.ToJson()))
+	if err := json.NewEncoder(w).Encode(firstAdminVisitMarketplaceObj); err != nil {
+		mlog.Warn("Error while writing response", mlog.Err(err))
+	}
 }