Generate secretsmith Vault configuration for routers via Salt

Summary:
This change adds to the Salt state carp (roles/router/carp/init.sls) a secretsmith configuration file
on routers, allowing the script from T2276 to authenticate to Vault using AppRole.

The configuration file (/usr/local/etc/secrets/carp-secretsmith.yaml) contains:

• Vault server URL
• AppRole credentials (role_id and secret_id) retrieved from Vault

Ref T2276

Test Plan:

• Applied state on router-002:
  
  salt 'router-002' state.apply roles/router test=True
  
  salt 'router-002' state.apply roles/router

• Applied state on router-003:
  
  salt 'router-003' state.apply roles/router test=True
  
  salt 'router-003' state.apply roles/router

Reviewers: dereckson, Duranzed

Reviewed By: dereckson

Subscribers: Duranzed, dereckson

Maniphest Tasks: T2276

Differential Revision: https://devcentral.nasqueron.org/D4031