(DOCS-8222)(Agent) Agent 6 installation (#23658)

* (DOCS-8222) Agent 6 installation commands

* Edits

* wip

* k8s and docker

* The rest of em

* small edit

* Edits

* Add new GPG keys

* Apply suggestions from code review

Co-authored-by: Esther Kim <[email protected]>
Co-authored-by: Marethyu <[email protected]>

* Edits

* Small edits

* Update content/en/agent/guide/install-agent-6.md

---------

Co-authored-by: Esther Kim <[email protected]>
Co-authored-by: Marethyu <[email protected]>

Author: 3 people

content/en/agent/guide/_index.md

@@ -42,6 +42,10 @@ cascade:
     {{< nextlink href="agent/guide/python-3" >}}Python 2 to 3 Custom Check Migration{{< /nextlink >}}
 {{< /whatsnext >}}
 
+{{< whatsnext desc="Agent 6 guides:" >}}
+    {{< nextlink href="agent/guide/install-agent-6" >}}Install Agent 6{{< /nextlink >}}
+{{< /whatsnext >}}
+
 {{< whatsnext desc="Agent 5 guides:" >}}
     {{< nextlink href="agent/guide/install-agent-5" >}}Install Agent 5{{< /nextlink >}}
     {{< nextlink href="agent/guide/agent-5-autodiscovery" >}}Autodiscovery in Agent v5{{< /nextlink >}}