[Monitoring] Fix issue with singular host config

[chrisronline]

Fixes #67373
Fixes #67668

The setup is something like this in your config:

monitoring.ui.elasticsearch.hosts: https://localhost:8200

If an array structure is not used, this code is not executed meaning the connection will use the default localhost:9200.

This seems like a bug with NP, but it also sounds like something we went through in the NP upgrade but I can't recall what came of that.

cc @restrry

[elasticmachine]

Pinging @elastic/stack-monitoring (Team:Monitoring)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: c35ddd1

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@elasticmachine merge upstream

[mshustov]

This seems like a bug with NP,

I don't think it's a problem with KP. createClient explicitly requires string[] as a valid interface. It has been discussed several times. 1 2
I'd suggest not to break type checking logic with any here

kibana/x-pack/plugins/monitoring/server/es_client/instantiate_client.ts

Line 19 in d6c0feb

elasticsearchConfig: any,

Since ElasticsearchConfig is not used in the monitoring plugin, createClient could have problems with ssl property initialized in the config class.

[chrisronline]

I synced with @restrry offline and we're going to wait until #67357 is in and update this PR to leverage the existing elasticsearch config class instead of defining anything custom.

[chrisronline]

Closing in favor of #68389