[Telemetry] Migrate to the new Elasticsearch client

[afharo]

Migration guide: https://github.com/elastic/kibana/blob/master/src/core/MIGRATION_EXAMPLES.md#elasticsearch-client; breaking changes: https://www.elastic.co/guide/en/elasticsearch/client/javascript-api/current/breaking-changes.html

Question regarding the callCluster method provided to the collectors: Should we replace it with { callCluster (with the deprecated flag), esClient (the new one), savedObjects }?

It is a breaking change, but it will also force the other plugins to adapt their logic to the new esClient if needed.

And, by providing savedObjects, collectors will have a "properly-scoped" SO client when retrieving the usage data.

[TinaHeiligers]

We can split this work into three four related issues to make it easier to handle:

1. Update the client and use internally (usage collectors and telemetry plugin)
2. Expose the new client as an additional parameter to creating a usage collector (related to enriching the APIs)
3. Replace callCluster and esClient with { callCluster, esClient } (and later on add the savedObjectsClient). This is a breaking change and will need to update all collectors using callCluster.
4. Handle the situation when monitoring is enabled: (monitoring provides the callCluster client factory) when we provide it in the usage collectors, we need to provide it in monitoring too. (dependency: [RFC] Kibana Telemetry & Monitoring)

[elasticmachine]

Pinging @elastic/kibana-telemetry (Team:KibanaTelemetry)

[TinaHeiligers]

We have a few issues related to enriching usage collection APIs. I've kicked off the work in #75875 and will build on that.

[TinaHeiligers]

#79044 handles step 3

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)