docs: Add matrix version between envoy and cilium

[ upstream commit 11e1bcc ]

This is to add a small docs for version matrix between Cilium and Cilium
envoy versions, which is useful with the upcoming work to move envoy
proxy out of Cilium agent container.

Co-authored-by: ZSC <zacharysarah@users.noreply.github.com>
Signed-off-by: Tam Mach <sayboras@yahoo.com>
Signed-off-by: Jussi Maki <jussi@isovalent.com>
Signed-off-by: Yutaro Hayakawa <yutaro.hayakawa@isovalent.com>

Documentation/concepts/security/proxy/envoy.rst

@@ -10,6 +10,12 @@
 Envoy
 =====
 
+Envoy proxy shipped with Cilium is built with minimal Envoy extensions and custom policy enforcement filters.
+Cilium uses this minimal distribution as its host proxy for enforcing HTTP and other L7 policies as specified in network policies
+for the cluster. Cilium proxy is distributed within the Cilium images.
+
+For more information on the version compatibility matrix, see `Cilium Proxy documentation <https://github.com/cilium/proxy#version-compatibility-matrix>`_.
+
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 Go Extensions
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