Add HIP-540: Change Or Remove Existing Keys From A Token

[SimiHunjan]

Problem

HIP-540 introduces new Hedera protobuf changes to TokenUpdateTransaction where the user will be able to remove keys that were initially set on the token.

HIP

• [x] https://hips.hedera.com/hip/hip-540

Hedera Protobuf

• [ ] (link Hedera protobuf PR when available)

Solution

• [ ] Design the feature
  • [ ] Add to the SDK references repository
• [ ] Implement design
• [ ] Add example

Alternatives

No response