Remote Cluster setup docs for ECK are outdated

[mmahacek]

The docs for configuring remote clusters, specifically for ECK at page https://www.elastic.co/docs/deploy-manage/remote-clusters/eck-remote-clusters have some issues that are confusing to users.

The page indicates that there are two security models, API key and TLS certificate. The TLS method is also documented as deprecated in v9+. There are steps on how to use the API key model when both clusters are in the same ECK environment, but in the section for connecting clusters outside of the same ECK environment, only TLS certificate instructions are provided. As the steps listed are only for the deprecated method, there are no valid steps for deploying remote clusters on v9.

This page needs an update to include the following:

• Steps for configuring remote clusters on different K8s environments using the API key method
• Notes on each of the TLS method sections reminding users that these steps only apply to v7/v8 deployments

[eedugon]

@mmahacek : a few quick questions to address this issue:

Steps for configuring remote clusters on different K8s environments using the API key method

Do you know if ECK supports the API Key method for clusters belonging to different k8s environment or operators? Have you confirmed this with devs?

Notes on each of the TLS method sections reminding users that these steps only apply to v7/v8 deployments

TLS method applies also to v9. Being deprecated doesn't mean that won't work on v9. It means that it will be removed in v10 and that users should start planning to move towards API key method.

Of course we have to recommend API key method over TLS, and we have to identify that TLS method is deprecated, but the steps apply to v7/8/9 deployments.

[mmahacek]

@eedugon Sorry for the delay in responding, I'm just getting back from PTO.
ECK doesn't directly support the API Key method. It requires configuring applying custom elasticsearch.yml settings based on docs at https://www.elastic.co/docs/deploy-manage/remote-clusters/remote-clusters-api-key, and adapting them as part of the K8s config.

I'm syncing back up with the CA/CE to verify the final config from a previous case, and will gather some sample configs to share.

[eedugon]

Don't worry @mmahacek : I had created an issue about this and @pebrc has already shared some light on it.
Check #1645 (comment)

We will try to improve the docs soon. If you want to share anything feel free to do it, but take in mind that this is a public repo, so maybe better to discuss in private, thanks!