Improve documentation for supported data sources

[andygrove]

What is the problem the feature request solves?

The documentation at https://datafusion.apache.org/comet/user-guide/datasources.html suggests that we do not yet support reading from S3 or the local file system, which is incorrect.

Also, it does not fully explain the difference between data sources that are supported fully natively (native_datafusion) versus the hybrid approach (native_comet and native_iceberg_compat).

Additionally, it does not mention Iceberg, which is a pretty big selling point for Comet.

Describe the potential solution

No response

Additional context

No response