gh-109945: Enable spec of multiple curves/groups for TLS

[planetf1]

• Issue #109945

Co-authored-by: Martin Schmatz

This change makes it possible to allow multiple groups to be specified in a colon separated string. See issues for more detail

The implementation choice is to modify the existing function rather than introduce a new one.

Initially opening as draft to check contributor guidelines, code layout etc.

• Issue: gh-109945