docs.thirdparty: Added LiveProxy
docs.thirdparty: Added LiveProxy

LiveProxy allows Streamlink to be easy accessible from **m3u** playlists,
it is also available for **Kodi Leia** and **Enigma2** devices.

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It is only meant for a local network.

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The argparser is copied from **streamlink_cli**,
this makes it easier to maintain and also allows the usage of all Streamlink commands.

Most of them will work, some not because they make no sense for LiveProxy.

**supported**

- Sideloading Plugins
- config files
- HLS, HTTP, HDS are supported.

**not supported**

- RTMP is not supported
- Dash will be supported at some point, but not right now.

It can play the stream or redirect the streaming url.

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Example of URLs

```
http://127.0.0.1:53422/play/?url=https%3A%2F%2Fwww.youtube.com%2Fuser%2Ffrance24

http://127.0.0.1:53422/301/?url=https%253A%252F%252Fwww.euronews.com%252Flive
```

A detailed guide can be found on the website.

gravyboat/streamlink,chhe/streamlink,beardypig/streamlink,wlerin/streamlink,beardypig/streamlink,melmorabity/streamlink,back-to/streamlink,streamlink/streamlink,streamlink/streamlink,bastimeyer/streamlink,melmorabity/streamlink,bastimeyer/streamlink,gravyboat/streamlink,wlerin/streamlink,chhe/streamlink,back-to/streamlink