Combines the following repositories into one: https://github.com/mattermost/mattermost-server https://github.com/mattermost/mattermost-webapp https://github.com/mattermost/focalboard https://github.com/mattermost/mattermost-plugin-playbooks
* migrate to CI pipeline to github actions * simplfy workflow --------- Co-authored-by: Akis Maziotis <36594156+phoinixgrr@users.noreply.github.com>