Agree on the scope and repositories for Apache Comet #6789

What is the problem the feature request solves?

Part of #6793.

The board resolution defines what the new project is responsible for, and the proposal lists the repositories that move to it. We need to agree on both before the DataFusion PMC votes on the proposal.

Describe the potential solution

Scope statement

DataFusion's resolution says "software related to an extensible query engine". Options for Comet:

1. "software related to accelerating Apache Spark using native, columnar execution"
2. "software related to Spark-compatible native query execution", which would also cover Spark-compatible components that are not part of the Spark plugin

Repositories and content

• Move apache/datafusion-comet in full and rename it to apache/comet. GitHub redirects the old URLs, as it did when the DataFusion repositories were renamed.
• Decide whether any other code moves. In [DISCUSS] Is Comet ready to move to top-level Apache Comet project? #5184, @comphead suggested moving the datafusion-spark crate from apache/datafusion to Apache Comet. That crate is released with DataFusion and Comet depends on it, so a move needs agreement from the DataFusion community. Code can move between ASF projects after the new project exists, so this decision does not need to block the resolution.
• Decide what happens to the Comet content that DataFusion hosts, such as the documentation at https://datafusion.apache.org/comet and the Comet posts on the DataFusion blog.

Additional context

Discussion: #5184

When DataFusion graduated from Arrow, the repositories were discussed in a separate thread.