Configure Mattermost Server on Startup

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OpsTool requires one bot account, incoming webhook and one slash command in the Mattermost server. This configuration is open to errors. To simplify configuration we can do it automatically at startup. For that:

1. Mattermost system admin will create a token with user creation, incoming webhook and slash command creation rights.
2. OpsTool will load required settings from configuration and if auto-configuration is enabled it will create or modify
   • Bot account
   • Incoming webhook (not limited to channel)
   • One slash command

Api Documentation: https://api.mattermost.com/