Merge --allow-unsupported-set into --unsupported-set-mode

[jasobrown-rs]

Description

--allow-unsupported-set was added to allow readyset is naively ignore any SET commands it could not process. About a year later, we introduced the --unsupported-set-mode flag and enum. One of the modes available is Allow, that mapped directly onto the existing --allow-unsupported-set.

Confusingly, we did not remove the older flag, and we did not allow setting --unsupported-set-mode allow. Let's reduce our cli flag burden and just merge the two behaviors, into the way it looks like it was intended to be.

[jasobrown-rs]

Duplicate of REA-4673

[jasobrown-rs]

Duplicate of #1354