Improve file name search to match partial words

[mattermod]

File search should be more forgiving with what is matched. ie if a file name was strawberryimage.jpeg but I search for strawberry, I would expect to get the result. Right now that result wouldn't be returned

Expected: When searching for files, always execute a wildcard search on the backend, even if the user does not enter a * in the search term

---

If you're interested please comment here and come join our "Contributors" community channel on our daily build server, where you can discuss questions with community members and the Mattermost core team. For technical advice or questions, please join our "Developers" community channel.

New contributors please see our Developer's Guide.

JIRA: https://mattermost.atlassian.net/browse/MM-35005

[kyeongsoosoo]

I'd like to work on this issue.