[Rust] Provide example of Flight server for DataFusion

[asfimport]

Now that IPC is in place and we have the Flight crate, it should be possible to build a working Flight server in Rust and call it from other languages such as Java.

This PR is for creating a DataFusion example that creates a Flight server capable of running SQL queries.

Reporter: Andy Grove / @andygrove
Assignee: Andy Grove / @andygrove

PRs and other links:

• GitHub Pull Request #6308

_{Note: This issue was originally created as ARROW-7684. Please see the migration documentation for further details.}

[asfimport]

Andy Grove / @andygrove:
Issue resolved by pull request 6308
#6308