chore(next): Type JSONSchema enum as unknown for better type safety

[sandrina-p]

Follow-up of #181, comment #181 (comment).

Watch this loom explaining why enum should be typed as unknown[] instead of any[].

TLDR: Internally we use enum to map it to some places that must be string. By using any, TS doesn't throw an error saying enum is not a string, which can lead to bugs if we don't pay attention (shown in Loom).
By typing enum as unknown[], TS calls our attention to it.

[lukad]

Late to the party, but thanks for the explanation! Overriding enum makes complete sense 👍