Generate markdown documentation for all CometConf entries

[andygrove]

What is the problem the feature request solves?

We should have a configuration reference page in our published documentation at https://datafusion.apache.org/comet/

Describe the potential solution

I propose that we write code to automatically generate a docs/sources/configs.md page based on the configuration entries specified in org.apache.comet.CometConf and execute this code from the maven build.

We will need to add this new page to the site index as well.

We can look at Apache Spark or NVIDIA Spark RAPIDS for inspiration on implementing this.

Additional context

No response