Quickstart k8s otel doc added

[eedugon]

Description

Adding a quickstart document for Unified Kubernetes Observability with EDOT.

Preview: https://observability-docs_bk_4488.docs-preview.app.elstc.co/guide/en/observability/master/monitor-k8s-otel-edot.html

The objective of this doc is to be a good entry point for this use case, considering that we have all details and detailed documents in elastic/opentelemetry repo: https://github.com/elastic/opentelemetry/tree/main/docs/kubernetes/operator

If possible I'd like to get a review by @mdbirnstiehl or @bmorelli25 before requesting the review by @mlunadia and @akhileshpok .

Initial concerns:

• The pre-requisites section looks a bit ugly and not very homogeneous.
• The title is a bit long, but I think this is what Miguel or Akhilesh wanted (we can check with them at a later stage).
• Should we add a similar doc to Serverless?

Documentation sets edited in this PR

Check all that apply.

• Stateful (docs/en/observability/*)
• Serverless (docs/en/serverless/*)
• Integrations Developer Guide (docs/en/integrations/*)
• None of the above

Related issue

Closes #4428

Checklist

• Product/Engineering Review
• Writer Review

Follow-up tasks

Select one.

• This PR does not need to be ported to another doc set because:
  • The concepts in this PR only apply to one doc set (serverless or stateful)
  • The PR contains edits to both doc sets (serverless and stateful)
• This PR needs to be ported to another doc set:
  • Port to stateful docs: <link to PR or tracking issue>
  • Port to serverless docs: <link to PR or tracking issue>

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[mergify]

This pull request does not have a backport label. Could you fix it @eedugon? 🙏
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.

[bmorelli25]

Looking good! A few grammar things

[eedugon]

@akhileshpok , @mlunadia : would you please review this PR? It will be the official quickstart / onboarding doc for k8s + OTel we have talked about for 8.16.

Note that this doc aims to not be too long, neither to provide / duplicate the same information we already have in our elastic/opentelemetry repository in markdown docs.

For example about instrumenting applications I've just referenced the GH repo

@mdbirnstiehl : feel free to review also if you like!

[mergify]

This pull request is now in conflict. Could you fix it @eedugon? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b otel_k8s_onboarding upstream/otel_k8s_onboarding
git merge upstream/main
git push upstream otel_k8s_onboarding

[eedugon]

conflict solved (hopefully) :-D

[eedugon]

@akhileshpok : I've talked with @bmorelli25 and we are going to add the information about being able to use on-premises clusters for this quickstart. We will add it in a different PR as we will update all quickstarts where this is applicable.

For serverless we will port this new doc to the serverless documentation as soon as it's approved.

[mdbirnstiehl]

Looks great! Just had a couple of suggestions.

[mdbirnstiehl]

Suggested change

	. Follow the on-screen instructions to perform the installation of all needed components.
	. Follow the on-screen instructions to install all needed components.

[mdbirnstiehl]

Suggested change

	* Optionally, for instrumenting applications, apply the corresponding `annotations` as showed in {kib}.
	* Optionally, for instrumenting applications, apply the corresponding `annotations` as shown in {kib}.

[mdbirnstiehl]

Suggested change

	For a more detailed description of the components and advanced configuration refer to the https://github.com/elastic/opentelemetry/blob/main/docs/kubernetes/operator/README.md[elastic/opentelemetry] GitHub repository.
	For a more detailed description of the components and advanced configuration, refer to the https://github.com/elastic/opentelemetry/blob/main/docs/kubernetes/operator/README.md[elastic/opentelemetry] GitHub repository.

[mdbirnstiehl]

Suggested change

	. Under the question *`What do you want to monitor?`* select **Kubernetes**, and then select the **OpenTelemetry: Full Observability** option.
	. Under *`What do you want to monitor?`*, select **Kubernetes**, and then select the **OpenTelemetry: Full Observability** option.

[mdbirnstiehl]

Suggested change

	* For applications instrumentation details, refer to https://github.com/elastic/opentelemetry/blob/main/docs/kubernetes/operator/instrumenting-applications.md[Instrumenting applications with EDOT SDKs on Kubernetes].
	* For application instrumentation details, refer to https://github.com/elastic/opentelemetry/blob/main/docs/kubernetes/operator/instrumenting-applications.md[Instrumenting applications with EDOT SDKs on Kubernetes].