rpm 4.14 (RHEL/CentOS/Rocky 8) cannot import an Ed25519 public key at all:
the import fails and package verification reports SIGNATURES NOT OK. RHEL 8
is supported until 2029 and is a realistic target for a signed package repo,
so the Ed25519 key excludes a large part of the rpm audience.
Publish an RSA-4096 signing key as 3proxy-release-key.asc and keep the old
Ed25519 key as 3proxy-release-key-ed25519.asc so artifacts up to 0.9.9 stay
verifiable. Workflows derive the key id from the imported secret key, so no
workflow change is needed.
