Description
salt-ssh generates salt-ssh.rsa key when first run, or when run later and the file doesn't exist. It ignores the priv setting in the master config for checking if it should generate the file. This forces a RSA key even if another key file exists already.

https://github.com/saltstack/salt/blob/master/salt/client/ssh/__init__.py#L314 is where priv is constructed, ignoring the roster_defaults and then a few lines later creating the "missing" file as a RSA key.

Setup
Debian package, LTS 3006

• on-prem machine
• classic packaging

config/master

root_dir: ./

file_roots:
  base:
    - ./srv/salt

pillar_roots:
  base:
    - ./srv/pillar

fileserver_backend:
  - roots

roster_defaults:
  priv: ./etc/salt/pki/master/ssh/salt-ssh.ed25519
  user: root

ssh_identities_only:  True
ssh_use_home_key: False

Steps to Reproduce the behavior
I can confirm that this config does use the correct SSH key (./etc/salt/pki/master/ssh/salt-ssh.ed25519) however it also creates ./etc/salt/pki/master/ssh/salt-ssh.rsa if it's missing, making it not clear that it's using the overridden key.

Expected behavior
Don't create ./etc/salt/pki/master/ssh/salt-ssh.rsa if the specified priv file exits. If it doesn't exist, it would be nice to create it with a key type other than RSA if this is easy enough to guess (like my example of ed25519 as the extension)

Versions Report

Salt Version:
          Salt: 3006.9
 
Python Version:
        Python: 3.10.14 (main, Jun 26 2024, 11:44:37) [GCC 11.2.0]
 
Dependency Versions:
          cffi: 1.16.0
      cherrypy: 18.6.1
  cryptography: 42.0.5
      dateutil: 2.8.1
     docker-py: Not Installed
         gitdb: Not Installed
     gitpython: Not Installed
        Jinja2: 3.1.4
       libgit2: 1.7.1
  looseversion: 1.0.2
      M2Crypto: Not Installed
          Mako: Not Installed
       msgpack: 1.0.2
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     packaging: 22.0
     pycparser: 2.21
      pycrypto: Not Installed
  pycryptodome: 3.19.1
        pygit2: 1.14.0
  python-gnupg: 0.4.8
        PyYAML: 6.0.1
         PyZMQ: 23.2.0
        relenv: 0.17.0
         smmap: Not Installed
       timelib: 0.2.4
       Tornado: 4.5.3
           ZMQ: 4.3.4
 
System Versions:
          dist: debian 12 bookworm
        locale: utf-8
       machine: x86_64
       release: 6.1.0-26-amd64
        system: Linux
       version: Debian GNU/Linux 12 bookworm

Additional context
Running salt-ssh hostname -v -ltrace --state-verbose=False test.ping 2>&1 |grep 'Executing command' allows us to verify the SSH command being run. We can see the correct SSH command (e.g. [TRACE ] Executing command: /usr/bin/ssh 1.2.3.4 -o KbdInteractiveAuthentication=no -o PasswordAuthentication=no -o GSSAPIAuthentication=no -o ConnectTimeout=65 -o Port=22 -o IdentityFile=./etc/salt/pki/master/ssh/salt-ssh.ed25519 -o User=root -o IdentitiesOnly=yes /bin/sh << 'EOF') using the specified keyfile, but the salt-ssh.rsa file has also been created.