Add IPv6 Control Decky plugin

[spmzt]

Add IPv6 Decky to Plugin Store

A plugin to control IPv6 on the Steam Deck from the Quick Access Menu.
SteamOS disables IPv6 by default and reverts the setting on every update.

Choose an IPv6 mode without leaving Game Mode:

• System default: the plugin changes nothing.
• Enabled: IPv6 is kept enabled.
• Disabled: IPv6 is kept disabled.
• IPv6 only: IPv6 is kept enabled and IPv4 is turned off on Wi-Fi and Ethernet.

Task Checklist

Developer

• I am the original author or an authorized maintainer of this plugin.
• I have abided by the licenses of the libraries I am utilizing, including attaching license notices where appropriate.
• Generative AI was NOT used to write a majority of the code I am submitting. (I'm not fluent with python anymore, so I wrote the main.py with AI, but I read it myself. The logic is clear and it solves a real problem I've myself.)

Plugin

• I have verified that my plugin works properly on the Stable and Beta update channels of SteamOS.
• I have verified my plugin is unique or provides more/alternative functionality to a plugin already on the store.

Backend

• No: I am using a custom backend other than Python.
• No: I am using a tool or software from a 3rd party FOSS project that does not have it's dependencies statically linked.
• No: I am using a custom binary that has all of it's dependencies statically linked.

Community

• I have tested and left feedback on two other pull requests for new or updating plugins.
• I have commented links to my testing report in this PR.

Testing

• Tested by a third party on SteamOS Stable or Beta update channel.

[github-actions]

Issues Found

• Neither testing box is present in your description. Please include one of them per the Markdown comment above the testing section.

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[spmzt]

#1127 (comment)
#1128 (comment)

[nicholasyoannou]

Can verify that the IPv6 Control plugin works as intended on SteamOS Stable and fixes a quirk with SteamOS (Steam Deck) where with dual-stack networks it only utilizes one (IPv4 or IPv6), disabling the other.

#1127 I'm introducing IPv6 connectivity support that allows IPv6 support as well, adding compatibility for this plugin.