RFE: known hosts certificate support

[scop]

Describe the bug
libssh2 does not appear to have support for certificates in known hosts, nor any other "markers" (things starting with @) based on a quick look at the code -- hope I didn't miss anything. Would be nice to have this.

To Reproduce
Use @cert-authority and perhaps @revoked lines in known_hosts; examples from the sshd man page:

   # A revoked key
  @revoked * ssh-rsa AAAAB5W...
  # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
  @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...

Expected behavior
Support host key verification using the above mentioned mechanism.

Version (please complete the following information):

• OS: [e.g. iOS] Any
• libssh2 version [e.g. 1.8.0] current git

Additional context
None

[stale]

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