[gator-permissions-controller] Terms of caveats on `erc20-token-revocation` permission are not correctly validated.

[jeffsmale90]

Description

When decoding a permission the terms of the caveats normally map to data on the permission request. In the case of the erc20-token-revocation this isn't the case, as the terms are implicit in the permission rather than representing conditions that the user / dapp can set.

Although decoding a permission is restricted to the gator permissions system, it's important that we correctly validate the terms to ensure that the delegation being signed is accurately represented to the user.

Add validation of caveat terms.