Document used port numbers

doc/ports

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+PORT NUMBERS USED OR RESERVED FOR USE ON DEUXFLEURS CLUSTERS
+
+Since we don't use Nomad's automatic port assignation (all ports are static
+and most jobs use network_mode = "host"), here is a list of used/reserved
+ports so that we can avoid conflicts when adding services.
+
+22      sshd
+24      dovecot lmtp
+25      postfix smtp
+53      unbound
+80      tricot
+143     dovecot imap
+389     bottin
+443     tricot
+465     postfix smtps
+587     postfix submission
+993     dovecot imaps
+1337    dovecot zauthoentication
+1728    nix-serve
+3719    grafana
+3900    garage S3 (prod)
+3901    garage RPC (prod)
+3902    garage web (prod)
+3903    garage admin (prod)
+3904    garage k2v (prod)
+3909    garage admin (staging)
+3990    garage S3 (staging)
+3991    garage rpc (staging)
+3992    garage web (staging)
+3993    garage k2v (staging)
+4317    jaeger
+4318    jaeger
+4646    nomad
+4647    nomad
+4648    nomad
+5432    psql_proxy
+5433    postgresql
+8008    synapse
+8080    jitsi video bridge (prod) / reserved (staging)
+8300    consul
+8301    consul
+8302    consul
+8501    consul
+8503    consul
+8600    consul
+8999    opendkim
+9090    prometheus
+9100    node_exporter
+9991    guichet