Fixes the client to setup SSL with the CA certificates for testing (#65598)

## Summary

Fixes the non-legacy ES test client to work with SSL.

Without this if you try to migrate `siem rules` or `alerting` or `CASE` or anything else that is using SSL based tests you get this error when trying to use the non-legacy:

```ts
// pull in non-legacy service for functional tests
const es = getService('es');
```

```ts
// use it somewhere where your config.ts is utilizing SSL in a functional test
// ...
```

In your console you get this error:

```ts
    ConnectionError: self signed certificate in certificate chain
          at onResponse (node_modules/@elastic/elasticsearch/lib/Transport.js:205:13)
          at ClientRequest.request.on.err (node_modules/@elastic/elasticsearch/lib/Connection.js:98:9)
          at TLSSocket.socketErrorListener (_http_client.js:401:9)
          at emitErrorNT (internal/streams/destroy.js:91:8)
          at emitErrorAndCloseNT (internal/streams/destroy.js:59:3)
          at process._tickCallback (internal/process/next_tick.js:63:19)
```

This fixes that by adding the CA certs from test to the ES test client.

Author: FrankHassanabad

test/common/services/elasticsearch.ts

@@ -18,15 +18,19 @@
  */
 
 import { format as formatUrl } from 'url';
-
+import fs from 'fs';
 import { Client } from '@elastic/elasticsearch';
+import { CA_CERT_PATH } from '@kbn/dev-utils';
 
 import { FtrProviderContext } from '../ftr_provider_context';
 
 export function ElasticsearchProvider({ getService }: FtrProviderContext) {
   const config = getService('config');
 
   return new Client({
+    ssl: {
+      ca: fs.readFileSync(CA_CERT_PATH, 'utf-8'),
+    },
     nodes: [formatUrl(config.get('servers.elasticsearch'))],
     requestTimeout: config.get('timeouts.esRequestTimeout'),
   });