SQ2-1065 - redesign API around Kira::V2::Client (v3.0 breaking)

[jmnsf]

Stacked on #13 (SQ2-1047), #12 (SQ2-1052), #11 (SQ2-1050), #10 (SQ2-1048). Top of the stack.

Major: changes the API surface to a more RESTful format. Instead of instancing a resource module with the API token etc, every resource is now reachable via a Kira::V2::Client class.

API

client = Kira::V2::Client.new(token: "...", base_url: nil)
interview = client.interview(id)

interview.applicants.create(first_name:, last_name:, email:, external_id: nil)
interview.webhooks.list
interview.webhooks.create(endpoint:, event_subscriptions:, secret:, active: true)
interview.webhooks.delete(uid)

[linear]

SQ2-1065

[migalvalm]

LGTM ✅ just a minor question