api: Nomad capabilities

[pkazmierczak]

Hackweek project from Feb 2024. Introduces a new API endpoint called /capabilities that reports what kind of features this Nomad server supports. Example:

$ curl localhost:4646/v1/capabilities|jq
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   124  100   124    0     0   104k      0 --:--:-- --:--:-- --:--:--  121k
{
  "ACL": true,
  "ACLEnabled": false,
  "ConsulVaultWI": true,
  "Enterprise": false,
  "NodePools": true,
  "OIDC": true,
  "WorkloadIdentity": true
}