Rspamd: milter headers

[chibenwa]

CF https://rspamd.com/doc/developers/protocol.html#milter-headers

add_headers: headers to add (object, indexed by header name)
remove_headers: headers to remove (object, indexed by header name)
change_from: change SMTP from value (plain string)
reject: custom rejection (plain string value), e.g. reject="discard" or reject="quarantine"
spam_header: custom spam header (plain string - header name)
no_action: instead of doing any action to a message, just add header X-Rspamd-Action equal to that action and accept message (boolean value)
add_rcpt: (from 1.8.0) add new recipients (array of strings)
del_rcpt: (from 1.8.0) delete recipients (array of strings)