Add parallelization to tootctl search deploy

[noellabo]

Parallelization makes index generation very fast.

[tribela]

On rake job, there are chewy:deploy and chewy:parallel:deploy.
Parallel is so fast, But sometimes it consume CPU very much and service gets unstable.
How about make it optional like tootctl search deploy -p=4?

[Gargron]

Hm, I wonder if --parallel should actually be --processes, because that's what the number controls through chewy/parallelize.