Register an OAuth client for this installation (RFC 7591 dynamic client registration) — step 1 of linking an existing MailKite account to your app. No pre-shared secret and no manual app review: you get a client_id back immediately and prove yourself with PKCE. Register once per install and keep the client_id.
HTTP: POST /oauth/register
oauth-client-response — see the oauth-client-response schema.
res = mk.registerOauthClient("client_name" => "MailKite for myapp.ai", "redirect_uris" => ["https://myapp.ai/settings/mailkite/callback"])