Allow to inspect Salt configuration

Summary:
Fetch servers list from the API (added in rAPI08d8932c6fe9)
and offers to print the server configuration.

The server configuration is generated by Salt using state.show_sls
and state.show_top (added in rOPSc0456415bc47).

Ref T1691

Test Plan: Browse https://infra.nasqueron.org/config

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1691

Differential Revision: https://devcentral.nasqueron.org/D2557