firewall: Read from rule map

[AOx0]

Add API methods in message, and handling in firewall to read existing rules

• message:
  • [x] Add methods to FirewallRequest
  • [x] Add responses to FirewallResponse
• firewall:
  • [x] Verify the rule id does exist (is initialized)
  • [x] Add, if necessary, response to message::FirewallResponse
• Methods:
  • [x] GET /firewall/rule/:id
  • [x] GET /firewall/rules