Adding error context in license validation (#29554)

While investigating https://mattermost.atlassian.net/browse/MM-61529,
I noticed that we weren't adding the internal error which made
it impossible to understand what was really happening.

```release-note
NONE
```

server/channels/api4/license.go

@@ -117,7 +117,7 @@ func addLicense(c *Context, w http.ResponseWriter, r *http.Request) {
 
 		canStartTrialLicense, err := lm.CanStartTrial()
 		if err != nil {
-			c.Err = model.NewAppError("addLicense", "api.license.add_license.open.app_error", nil, "", http.StatusInternalServerError)
+			c.Err = model.NewAppError("addLicense", "api.license.add_license.open.app_error", nil, "", http.StatusInternalServerError).Wrap(err)
 			return
 		}