Improve security for the `PYTHON_REDMINE_KEY` key
Now that we have a better understanding of private packages (cf. https://gitlab.teklia.com/workers/dan/-/merge_requests/142), we know that it is better to use:
- a
.netrc
file so that we only have to copy the key once for ever - use docker
--secret
for better security
We need to split the existing CI variable PYTHON_REDMINE_KEY
to have PYTHON_REDMINE_LOGIN
and PYTHON_REDMINE_PWD