Move DataFusion cli/repl to own crate

[Dandandan]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
The Datafusion cli/repl functionality now lives inside the DataFusion tree.
This has two main implications:

• Building DataFusion fetches extra dependencies (clap rustyline and transitive dependencies) unneeded for the rest of DataFusion, slowing the development cycle down a bit (mainly for clean builds).
• Installing the binary using cargo is a bit more cumbersome, cargo install datafusion --bin datafusion-cli --release
• dependency constraints on the cli dependencies potentially can cause conflicts for DataFusion consumers

Describe the solution you'd like
Move the datafusion-cli to the root dir.
Publish the crate to crates.io as datafusion-cli. The tool now can be installed using cargo install datafusion-cli --release and now lives outside of the DataFusion crate.

Describe alternatives you've considered
Keep structure as is.

Additional context

[houqp]

+1 these cli dependencies could cause unnecessary dependency conflicts for downstream datafusion consumers as well.

[Dandandan]

That's a good one @houqp I'll add that as well.

[alamb]

I think this is a good idea. We might even get away without publishing the cli as a separate crate unless we have people who use it (perhaps we can pull the binary out and then publish a new crate if anyone wants it)

[andygrove]

I also filed apache/datafusion-ballista#455 for publishing the DataFusion CLI as a Docker image