[enterprise-4.21] [OCPBUGS#77520]: Add note about EndpointSlice limitations to commatrix plugin docs

[lcavalle]

This is a manual cherry-pick of #114644

/assign gaurav-nelson

Version(s):
4.21

Issue:
https://redhat.atlassian.net/browse/OCPBUGS-77520

Link to docs preview:

QE review:

• QE has approved this change.

Additional information:
Manual cherry-pick because the automatic cherry-pick failed due to a merge conflict in modules/network-commatrix-plugin-intro.adoc. The 4.21 branch did not have the pre-existing paragraph about EndpointSlice/firewall that was rewritten on main, so the changes were applied manually.

Rewrites the EndpointSlice limitation paragraph in the commatrix plugin intro module (modules/network-commatrix-plugin-intro.adoc) to clarify:

• The communication matrix uses EndpointSlice objects for port discovery
• Kubernetes creates EndpointSlice objects automatically for each Service object
• All core OpenShift ports are fully covered starting with OCP 4.21
• Non-core Operators or software without a Service object do not appear in the matrix
• The --host-open-ports flag captures actual listening ports not defined through Service or EndpointSlice objects
• The generated diff file shows differences between intended and actual state

Also adds a brief NOTE to the install module (modules/network-commatrix-plugin-install.adoc) highlighting the key limitation and the --host-open-ports workaround.

[ocpdocs-previewbot]

🤖 Mon Jul 20 14:14:08 - Prow CI generated the docs preview:

https://115813--ocpdocs-pr.netlify.app/openshift-enterprise/latest/installing/install_config/configuring-firewall.html

[openshift-ci]

@lcavalle: all tests passed!

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