add isJWT validation

[Sevi7]

isJWT() can be useful for validating user tokens sent in querystring parameters in WebSocket connections

[colinhacks]

Probably best achieved with .regex()

[renatoargh]

You can use .refine(value => validator.isJWT(value)) where validator comes from https://www.npmjs.com/package/validator

[stale[bot]]

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