Suggestions for the company database

Added a an actual form for cdb suggestions. The suggestions are posted as an issue (currently to a test project, so feel free to test to your heart's content; I will change that to datenanfragen/companies once the MR is merged). An actual PR would of course be nicer but also much more annoying (and potentially costly) to implement. I think issues are a good compromise for now. If we actually see heavy use in the future, we can always improve later.

I decided to implement the 'gateway' to the GitHub API via AWS Lambda and AWS API Gateway through the Serverless framework (see datenanfragen/edit-api for the code) because that is a) easy and practically maintenance-free and b) we will definitely fall into the free usage tier unless we get a ridiculous amount of contributions.
Thanks to the Serverless framework, it is trivial to move to another Lambda provider in the future. Of course, we can also easily host the code ourselves, if we so decide.