docs: clarity around http filter ordering (#11057)

I still had an arcane mental model (pre https://github.com/envoyproxy/envoy/pull/5955) where both decoder and encoder filters where invoked in the same order as the configuration order. My mind was so used to this I even failed to notice the code that prepends encoder filters into the encoder_filters_ list in the conn manager. These documentation additions are trying to make the behavior as explicit as possible so others are not confused.

Risk Level: low - doc updates, no behavior change.
Docs Changes: updated inline comments in the code I failed to notice, and in the project docs.

Signed-off-by: Jose Nino <jnino@lyft.com>

Mirrored from https://github.com/envoyproxy/envoy @ 4abe685446316f79ba1627cf830f0c0d398abdaf

envoy/config/filter/network/http_connection_manager/v2/http_connection_manager.proto

@@ -262,8 +262,8 @@ message HttpConnectionManager {
   }
 
   // A list of individual HTTP filters that make up the filter chain for
-  // requests made to the connection manager. Order matters as the filters are
-  // processed sequentially as request events happen.
+  // requests made to the connection manager. :ref:`Order matters <arch_overview_http_filters_ordering>`
+  // as the filters are processed sequentially as request events happen.
   repeated HttpFilter http_filters = 5;
 
   // Whether the connection manager manipulates the :ref:`config_http_conn_man_headers_user-agent`

envoy/extensions/filters/network/http_connection_manager/v3/http_connection_manager.proto

@@ -263,8 +263,8 @@ message HttpConnectionManager {
   }
 
   // A list of individual HTTP filters that make up the filter chain for
-  // requests made to the connection manager. Order matters as the filters are
-  // processed sequentially as request events happen.
+  // requests made to the connection manager. :ref:`Order matters <arch_overview_http_filters_ordering>`
+  // as the filters are processed sequentially as request events happen.
   repeated HttpFilter http_filters = 5;
 
   // Whether the connection manager manipulates the :ref:`config_http_conn_man_headers_user-agent`

envoy/extensions/filters/network/http_connection_manager/v4alpha/http_connection_manager.proto

@@ -263,8 +263,8 @@ message HttpConnectionManager {
   }
 
   // A list of individual HTTP filters that make up the filter chain for
-  // requests made to the connection manager. Order matters as the filters are
-  // processed sequentially as request events happen.
+  // requests made to the connection manager. :ref:`Order matters <arch_overview_http_filters_ordering>`
+  // as the filters are processed sequentially as request events happen.
   repeated HttpFilter http_filters = 5;
 
   // Whether the connection manager manipulates the :ref:`config_http_conn_man_headers_user-agent`