Implement From<bool> trait for Value

[edgedb-cla[bot]]

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[Dhghomon]

Hi @hongquan, I'd been meaning to add a few From impls and had just merged another PR of mine so thought I would do it separately on a branch from master which includes the From you suggested. Thanks!

https://github.com/edgedb/edgedb-rust/commit/67f89b31ee5518611a788d3842f01be2eba9eb48#diff-87d4558ffc6631071aadde9c152899530882adabb3428350c3c4f054d0d3a985R168

[hongquan]

Thanks