[Networking] Doxygen (#7030)

* [Networking] Doxygen

* Lint cause my autolinter is broken lol

* Update.

* Update Doxyfile

Co-authored-by: tooomm <tooomm@users.noreply.github.com>

* Alphabetical ordering

Co-authored-by: tooomm <tooomm@users.noreply.github.com>

* Add new card art rule comment

* move filter program into doxygen folder

* [Networking] Doxygen


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Co-authored-by: Lukas Brübach <lukas.bruebach@bdosecurity.de>
Co-authored-by: tooomm <tooomm@users.noreply.github.com>
Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

doc/doxygen/extra-pages/developer_documentation/network/protocol/index.md

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+@page developer_reference_protocol Protocol (Overview)
+
+For an overview of the protocol used by the Cockatrice client and server, see:
+
+- @subpage developer_reference_protocol_overview
+- @subpage protocol_game_command
+
+For client → server communication, see:
+
+- @subpage protocol_command_container
+
+For server → client communication, see:
+
+- @subpage protocol_server_message
+- @subpage protocol_response