[Backport 7.x] Export a kibana restricted type definition (#1248)

Co-authored-by: Tomas Della Vedova <delvedor@users.noreply.github.com>

test/types/client.test-d.ts

@@ -4,7 +4,7 @@
 
 import { expectType } from 'tsd'
 import { Client, ApiError, ApiResponse, RequestEvent, ResurrectEvent } from '../../'
-import { TransportRequestCallback, TransportRequestPromise } from '../..//lib/Transport';
+import { TransportRequestCallback, TransportRequestPromise } from '../../lib/Transport'
 
 const client = new Client({
   node: 'http://localhost:9200'
@@ -120,4 +120,4 @@ client.on('resurrect', (err, meta) => {
   } catch (err) {
     expectType<any>(err)
   }
-}
+}