Define how we manage new contributions and issues in wis2box

[maaikelimper]

Dear Tom, could you help provide some guidance (to be documented once defined) with regards the following:

• how do we track issues from images built in repository outside of this one, namely (wis2box-api, wis2box-ui, wis2box-webapp, wis2downloader). Do we reference or move issues from these other repo's to the main repo ? Or should we move to have a "wis2box-project" to associate issues from different repositories to ?
• how do we manage contributions and issues from GitHub-users outside of the known team of developers ? (I add the label "security" as managing who can contribute to our code impacts security of our codebase)

[tomkralidis]

• close issue trackers on wis2box-*
• updated READMEs to point to wmo-im/wis2box/issues for project control/issue management (@tomkralidis)

[tomkralidis]

Closed issue trackers, wikis and updated READMEs in:

• wis2box-auth
• wis2box-api
• wis2box-ui
• wis2box-webapp

[tomkralidis]

For managing contributions:

• we have a CONTRIBUTING.md which is also referred to from https://docs.wis2box.wis.wmo.int/en/1.0b8/community/contributing.html for good measure.
• contributions from anyone outside the core committers are subject to PR review by all core committers

TODO: discuss committer access (@tomkralidis @efucile)