Export a kibana restricted type definition

[delvedor]

While working on #1243 and elastic/kibana#69905 we have decided that we should start shipping a restricted type definition file for Kibana, which hides the snake_cased and callbacks style APIs.

The type can be used as follows:

import { Client } from '@elastic/elasticsearch'
import { KibanaClient } from '@elastic/elasticsearch/api/kibana'

const client: KibanaClient = new Client({
  node: 'http://localhost:9200'
})

[pgayvallet]

This LGTM regarding our needs.

[mshustov]

nit: it's easy to forget to update length if we change start token. Do you think you could you refer it explicitly?

const startToken = '/* GENERATED */';
let startPosition = oldTypeDefString.indexOf(startToken)
let newTypeDefString = oldTypeDefString.slice(0, start + startToken.length) + ...

[delvedor]

I don't expect it to change, also, we could still forget to update it here :D

[sebelga]

@delvedor Jumping in on @restrry comment. The recommended change is not only to cover the case where "start token" would change, but also to avoid "magic" number as per our styleguide (https://github.com/elastic/kibana/blob/master/STYLEGUIDE.md#magic-numbersstrings).
When I read 15 it does not mean anything, when I read startToken.length it is explicit what it is. Just my 2 cents 😊