Refactor response status textToPost

[jfrerich]

Summary

The updateEventsInDatabase() function could benefit from refactoring. This ticket is a request to create a utility function to share this duplicated code.

Here is the relevant code that needs to be modified:
https://github.com/mattermost/mattermost-plugin-google-calendar/blob/master/server/utils.go#L202
https://github.com/mattermost/mattermost-plugin-google-calendar/blob/master/server/utils.go#L372

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