[EBT] ElasticV3-Server - Check connectivity as soon as optIn(true) is called

[afharo]

Summary

Resolves #135647.

The shipper ElasticV3-Server now reacts to OptIn value changes to check connectivity as soon as it's set. Instead of waiting 1 minute for the next tick of the timer.

While I was at it, I fixed a couple of gotchas:

• We used concatMap in the connectivity checks. It could trigger multiple requests at the same. For a connectivity check, it makes sense to trigger only one at a time, so I switched it to exhaustMap.
• I split a very long test into smaller chunks. I recommend using the Hide whitespace changes toggle when reviewing.

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

Risk Matrix

Delete this section if it is not applicable to this PR.

Before closing this PR, invite QA, stakeholders, and other developers to identify risks that should be tested prior to the change/feature release.

When forming the risk matrix, consider some of the following examples and how they may potentially impact the change:

Risk	Probability	Severity	Mitigation/Notes
If Kibana sends optIn(true) too many times, we might trigger requests more often.	Low	Medium	That call is triggered by user interaction. I would not expect them to call it that often to hurt their own cluster. However, if we really think it could be an issue, we can add .pipe(distinct()) to only react to changes in the value.

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[elasticmachine]

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

[TinaHeiligers]

@elasticmachine merge upstream

[TinaHeiligers]

LGTM

[kibana-ci]

💚 Build Succeeded

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Metrics [docs]

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
@kbn/analytics-shippers-elastic-v3-server	15	18	+3

Total ESLint disabled count

id	before	after	diff
@kbn/analytics-shippers-elastic-v3-server	15	18	+3

History

• 💚 Build #59812 succeeded 3814614

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@elasticmachine merge upstream