Update infrastructure monitoring docs about containers

[dedemorton]

Closes #3745

Preview links:

• https://observability-docs_bk_4186.docs-preview.app.elstc.co/guide/en/observability/master/view-infrastructure-metrics.html
• https://observability-docs_bk_4186.docs-preview.app.elstc.co/guide/en/observability/master/container-metrics.html

TODO after merging:

• Port changes to serverless Port #4186 to serverless #4225
• Set up redirect for changed path

[github-actions]

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[mergify]

This pull request does not have a backport label. Could you fix it @dedemorton? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-/d./d is the label to automatically backport to the /d./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[jennypavlova]

Nice 👏 thank you!
One note regarding the metrics - we also show Network and Disk now:

(Not sure if we want to include it in the screenshots - cc @roshan-elastic)
Overall LGTM but I am leaving the final review to @roshan-elastic

[dedemorton]

One note regarding the metrics - we also show Network and Disk now

@jennypavlova Good point! I didn't see those tabs because I was looking at an environment that was all K8s. I think I should show those tabs.

[dedemorton]

@jennypavlova or @roshan-elastic I have a few follow-up questions after applying the Jenny's changes:

• Can you point me to an environment that shows docker metrics? I've only been able to find oblt environments with K8s. I've temporarily used the screenshot that Jenny created to show all the metrics, but I think I might also need to redo the overview screenshot.
• Are network and disk metrics shown in 8.15 as well as 8.16?
• I don't see disk metrics listed for Docker in this document. Should it be? If so, I think we need to update the topic about docker metrics, too.

[roshan-elastic]

Can you point me to an environment that shows docker metrics? I've only been able to find oblt environments with K8s. I've temporarily used the screenshot that Jenny created to show all the metrics, but I think I might also need to redo the overview screenshot.

Think I found something on edge:

Are network and disk metrics shown in 8.15 as well as 8.16?

Checking on the demo cluster (8.15), it doesn't look like it. Looks like 8.16 only.

I don't see disk metrics listed for Docker in this document. Should it be? If so, I think we need to update the topic about docker metrics, too.

Good catch. Added it now.

One note - it looks like the docker metrics are being used even for containerd containers - this looks like a bug so I'd ignore documenting Kubernetes network/disk metrics for now.

@jennypavlova - Could you confirm if this is a bug? I know we're going to clean all of this up in https://github.com/elastic/observability-dev/issues/3470

[dedemorton]

This PR targets 8.15, so I am going to remove mention of network and disk metrics for now.

I've opened a separate issue for 8.16 to make sure network and disk metrics get added when we're ready to document them.

[colleenmcginnis]

Just a tiny suggestion.

[colleenmcginnis]

🐥