Backport tests from upstream commit 3d1ef3a15c3 (adapted for PG16):
- Test that invalid ssl_ecdh_curve values (colon-separated) are rejected
- Test that valid colon-separated groups are accepted
- Add multi-group configuration to SSL test infrastructure
Resolves: RHEL-119229
Co-authored-by: Cursor <cursoragent@cursor.com>
