Add ShadowDeck plugin. Plagin for ShadowSocket

[tikh-iv]

Add ShadowDeck to Plugin Store

ShadowDeck allows you to access ShadowSocks connection for whole system. ShadowDeck establishes a full Shadowsocks connection. This can be particularly useful in countries with network censorship. It differs from TunnelDeck in that TunnelDeck only manages OpenVPN or WireGuard connections from the Network Manager, whereas ShadowDeck uses sing-box app to establish connection.

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.

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.
• Yes: I am using a tool or software from a 3rd party FOSS project that does not have it's dependencies statically linked. https://github.com/SagerNet/sing-box
• No: I am using a custom binary that has all of its 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

• Both testing boxes are present in your description. Please remove one of them per the Markdown comment above the testing section.

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[EMERALD0874]

Both test reports are invalid as they do not use the required format. PR description also needs to be fixed (see @github-actions comment).

[tikh-iv]

1st review
2nd review

[EMERALD0874]

LGTM for testing