Motivation:

CORs is a technique that uses additional HTTP headers
to inform browsers to give a client application at a
particular origin access to requested resources at a
different origin. This was previous implemented but
needed some few adjustment to make it work.

Modification:

- Change the property name for allowed origin from
    cerebrum.allowed.client.origins to cerebrum.allowed.origins
    Hence it can be set in the command line as follow:
    `java -jar --cerebrum.allowed.origins=<comma-seperated-values>`
- Add OPTIONS method to the list of allowed methods and obtain
    the value of the property: `cerebrum.allowed.origins`

Result:

CORs now works

Target: master
Review: https://gitlab.hzdr.de/hifis-technical-platform/helmholtz-cerebrum/-/merge_requests/36