add DeckScreenshotManager

[codehz]

Screenshot Uploader

Valve does not implement auto-upload screenshot for us, so I added it.

See: https://steamcommunity.com/app/1675200/discussions/2/6117591738155117046/

It is a simple plugin, no custom backend code is needed, all functionality is implemented in js (except for saving/loading setting, which is implemented in python), reuse SteamClient API.

Do not confuse with the Shotty plugin, since it is used to link screenshot to Picture folder.

Checklist:

Developer Checklist

• 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 Checklist

• 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 alternatively provides more/alternative functionality to a similar plugin already on the store.

Plugin Backend Checklist

• 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.

Testing

• Tested on SteamOS Stable/Beta Update Channel.

[TrainDoctor]

@SteamDeckHomebrew/decky-testers ready for testing.

[nabel0]

Tested and works fine on SteamOS Stable/Beta Update Channel.