[Data] Improve error message when reading HTTP files

[bveeramani]

Why are these changes needed?

If you try to read HTTP files with Ray Data, you get this error message if fsspect[http] isn't installed:

Please install fsspec to read files from HTTP.

This PR updates the error message to clarify that you need the http extra:

To read files from HTTP, run pip install fsspec[http].

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