Add External Engine API methods

[joshka]

Builds on #12 - so if reviewing just read the last 2 commits:

• feat: add external engine API methods https://github.com/ion232/lichess-api/pull/14/commits/5f7bef4a02d3d21e55358e4d9f53d0cc0e230ce8
• feat: add engine analyse https://github.com/ion232/lichess-api/pull/14/commits/bc579558c61b55ebc2f3cb2eda5d45434ed26b24

WORKING:

• create
• update
• list
• get
• delete

TODO:

• /engine/{id}/analyse gives a 404 currently (https://lichess.org/api#tag/External-engine/operation/apiExternalEngineAnalyse)
• https://lichess.org/api#tag/External-engine/operation/apiExternalEngineAcquire
• https://lichess.org/api#tag/External-engine/operation/apiExternalEngineSubmit (requires streaming POST - so this might be a bit more effort than the other methods)

[joshka]

Rebased on main and cleaned up the commits - I haven't looked at this in a while, so I've forgotten where it was up to. Just pushing what I had locally

[ion232]

I've just pushed some changes that add support for other domains in a way that's different to yours. The domain is now part of the request itself, but defaults to lichess.org, so it isn't really noticeable unless you need to change it. You'll have to update your code to use that for the engine.lichess.ovh endpoints

[joshka]

Neat - thanks for that :)