feat: add snippets plugin

[xXJSONDeruloXx]

Add Snippets to Plugin Store

This is a simple plugin that lets you create "snippets" for launch commands you typically add to steam launch args, such as SteamDeck=0 %command%. There is a toggle to append the %command% at the end of the snippet for added convenience. On selection of the snippet, it gets coppied to your clip board, ready to paste into the launch args line.

You can add your own snippets, and optionally name them, then edit or delete them, or reset to default.

This is functionally different than the Decky Clipboard plugin as this does not link your clipboard across devices, rather it lets you curate a set of commonly used strings, to reduce the PITA that typing with the deck keyboard can be.

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.
• 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.

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[EMERALD0874]

I'm discussing this with the team since the use case seems very specific, and I'd like to know if it could be implemented in another plugin or with additional options. We'll get back to you once we have feedback, if any.

[xXJSONDeruloXx]

@EMERALD0874 custom launch args are a pretty regular thing for myself or those who like to mod, or apply protondb fixes occasionally. Let me know how the discussions go and if there's any recommendation on consolidation