Add Backburner plugin

[Xander567]

Add Backburner to Plugin Store

Backburner is a games suggestion site that gives suggestions on what to play next. It uses a bunch of data such as HLTB, Protondb, tags and genres, along with users play time to find out what they like and what they don't and then tries to suggest it. Users can setup an LLM and feed in mood suggestions such as "I'm having a shit day at work, gimme a 45 minute quick game", and it'll use your library to make a suggestion.

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.

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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