Integrate SVMON with Mattermost

We have to integrate SVMON with Mattermost, either via Message bus or directly via APIs.

The idea is if there is a change in version detected in SVMON, the SVMON updates the dedicated Channel in Mattermost with information which provider, which service and which service component was updated. For example the b2safe updates should be published in b2safe broadcast channel: https://chat.eudat.eu/eudatops/channels/eudat-broadcast-b2safe.

This feature to be implemented after history feature is working. We probably would need a test mattermost instance for that, I will take care of preparing test mattermost instance.