Step ca sign doesn't allow CSR having empty subject with valid sans using acme provisioner

[avineshk09]

Step ca sign command doesn't allow CSR with empty subject with valid sans using acme provisioner.

step ca sign acmet1.localstepca.com.csr acmet1.localstepca.com.crt --acme https://localstepca.com/acme/acme/directory
error creating new ACME order: The request message was malformed

step ca sign acmet1.localstepca.com.csr acmet1.localstepca.com.crt --provisioner acme
✔ What DNS names or IP addresses would you like to use? (e.g. internal.smallstep.com): acmet1.localstepca.com
✔ Provisioner: acme (ACME)
error creating new ACME order: The request message was malformed

DNS names validation failed at Step ca acme server:

WARN[58728] duration="746.54µs" duration-ns=746540 error="invalid DNS name: " fields.time="2024-09-23T11:43:40+05:30" method=POST name=ca nonce=TjBXeFBONFVheUs0TnlHN1I5WHhvbkc3N05PbWRleDE path=/acme/acme/new-order protocol=HTTP/1.1 referer= remote-address=127.0.0.1 request-id=42498344-ef1a-41e9-901c-2f47b389ee5b response="{"type":"urn:ietf:params:acme:error:malformed","detail":"The request message was malformed"}" size=93 status=400 user-agent="Smallstep CLI/0.27.2 (darwin/amd64)" user-id=

This is happening due to cli is adding empty subject to dns identifiers in new-order acme request here:
https://github.com/smallstep/cli/blob/cd6758c91df547d0039768c9413b94e96e55ff24/utils/cautils/acmeutils.go#L376C11-L382C4

Sample CSR to reproduce:
acmet1.localstepca.com.csr.txt

Fix would be to add subject commonName from CSR only if it is not empty.