vici: flush-certs command flushes certificate cache

When fresh CRLs are released with a high update frequency (e.g.
every 24 hours) or OCSP is used then the certificate cache gets
quickly filled with stale CRLs or OCSP responses. The new VICI
flush-certs command allows to flush e.g. cached CRLs or OCSP
responses only. Without the type argument all kind of certificates
(e.g. also received end entity and intermediate CA certificates)
are purged.

src/libcharon/plugins/vici/ruby/lib/vici.rb

@@ -448,6 +448,12 @@ module Vici
       @transp.request("get-conns").root
     end
 
+    ##
+    # Flush credential cache.
+    def flush_certs((match = nil)
+      check_success(@transp.request("flush-certs", Message.new(match)))
+    end
+
     ##
     # Clear all loaded credentials.
     def clear_creds()