Problem: filetype: SSH keys and related filetypes not recognized
Solution: Detect sshpublickey, sshknownhosts sshauthorizedkeys and
sshallowedsigners filetypes, add syntax scripts for those
filetypes (Fionn Fitzmaurice)
This adds syntax highlighting for SSH public keys, as well as related
filetypes derived from this (SSH authorized keys, SSH known hosts and
SSH allowed signers).
Also add filetype detection based on the path and name.
closes: vim/vim#206356e66ebc0fd
Co-authored-by: Fionn Fitzmaurice <git@fionn.computer>
