Extract project maintainers from MAINTAINERS file

[hjacobs]

It would be awesome to get the maintainers (via REST API) of all repositories. Example MAINTAINERS file: https://github.com/zalando-stups/fullstop/blob/master/MAINTAINERS

This information could be displayed but also used to check for non-maintained projects and to do custom scripting ("give me all projects I'm maintaining").

[hjacobs]

Necessary steps:

• scheduled job needs to collect maintainers from MAINTAINERS file
• maintainers should be part of the project model
• REST API needs to return maintainers property containing a list of strings

[hjacobs]

Deployed LIVE, check https://catwatch.opensource.zalan.do/projects?organizations=zalando,zalando-stups,zalando-techmonkeys&limit=6&offset=0&sortBy=-score