Transfer the issues from -sec to pypsa-earth

[davide-f]

Describe the feature you'd like to see

As agreed with @hazemakhalek , we shall transfer the issues from this repo to -sec.
Options are available as mentioend here:
https://docs.github.com/en/issues/tracking-your-work-with-issues/administering-issues/transferring-an-issue-to-another-repository

Shall we move all issues (open and closed), only the open ones? [best the first option, if the transfer can be done in bulk, not one by one]
The "when to act" must be agreed with the -sec team first.

This issue is to give visibility and discuss on the plan :)