Add Pyodide lockFileURL option

[rth]

Related to the discussion pyodide/pyodide#3573 by @bollwyvl once we have the ability to create a custom pyodide-lock.json we need to have some way to point this kernel to use it.

Supposing this pyodide-lock.json is created alongside other JupyterLite files and deployed with those, I'm also not sure how that URL should look like: just a relative path?

[github-actions]

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[rth]

Though looking at #29 @bollwyvl are you saying that {lite_dir}/pypi/repodata.json (now {lite_dir}/pypi/pyodide-lock.json) would be a hardcoded path, and that this configurability is not needed? Either way should be fine.

In which case I can close this.

**Edit:**also, do I also need to add it to packages/pyodide-kernel-extension/schema/kernel.v0.schema.json to avoid?

error TS2741: Property 'pyodideLockFileURL' is missing in type '{ baseUrl: string; pyodideUrl: string; indexUrl: string; 
pipliteWheelUrl: string; pipliteUrls: string[]; disablePyPIFallback: boolean; location: string; mountDrive: boolean; }' but required in type 'IOptions'.

[bollwyvl]

As of #103, pyodideLockURL (and JSON-compatible friends in loadPyodide(options)) are now available to be configured in jupyter-lite.json, which should ship as part of jupyterlite-pyodide-kernel 0.3.0.

Minor upstream note: moving the options typing into a named interface would make this just that much better for downstreams! I didn't fully grok the ts-in-js toolchain to make that happen, however...

Looking further down the line, these options should put enough pieces in place to support an addon that:

• uses e.g. a browser to do a real solve of the lock from micropip.freeze
• grabs all the wheels
• backfills the import names with pyodide-lock

I had started them in the same PR, but it became clear that this would add rather a lot of complexity, so will probably try to land it as another installable package, but theoretically could become an [lock] extra of this package.