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ARROW-12437: [Rust] [Ballista] Create DataFusion context without repartition

Ballista plans must not include `RepartitionExec` because it results in incorrect results. Ballista needs to manage it's own repartitioning in a distributed-aware way later on. For now, we just need to configure the DataFusion context to disable repartition.

Closes #10086 from andygrove/ballista-no-repartition

Authored-by: Andy Grove <andygrove73@gmail.com>
Signed-off-by: Andy Grove <andygrove73@gmail.com>