Changing mattermost-auth method to work based on shared database access (#335)

* Improving mattermost auth implementation

* Making mattermost-auth based on shared database access

* Reverting unneeded changes in the config.json file

* Fixing tiny problems

* Removing the need of using the mattermost session token

* Fixing some bugs and allowing to not-bind the server to any port

* Small fix to correctly get the templates

* Adding the mattermost-plugin code inside focalboard repo

* Adding a not working code part of the cluster websocket communication

* Updating the mattermost version

* Adding the cluster messages for the websockets

* Updating to the new node version

* Making it compatible with S3

* Addressing some tiny problems

* Fixing server tests

* Adds support for MySQL migrations and initialization

Co-authored-by: Miguel de la Cruz <miguel@mcrx.me>

server/integrationtests/clienttestlib.go

@@ -34,6 +34,7 @@ func getTestConfig() *config.Configuration {
 		DBConfigString: connectionString,
 		DBTablePrefix:  "test_",
 		WebPath:        "./pack",
+		FilesDriver:    "local",
 		FilesPath:      "./files",
 	}
 }