[Greenfield]: Add support for Delegate and Undelegate messages

[satoshiotomakan]

Description

Add support for MsgDelegate and MsgUndelegate.

TODO

• Broadcast valid transactions and fix the GreenfieldSigner.SignMsgDelegate test.
  There is a properly generated, signed and encoded transaction that failed during the execution: https://greenfieldscan.com/tx/EC8C246841DAAEC9445557073B538E011C48AD9F479B1549E5F000CB4BF57E2D
  The problems seems to be in the incorrect validator address.
• Add the GreenfieldSigner.SignMsgUndelegate C++ test.
• Add Android, Swift tests

How to test

Types of changes

Checklist

• Create pull request as draft initially, unless its complete.
• Add tests to cover changes as needed.
• Update documentation as needed.
• If there is a related Issue, mention it in the description.

If you're adding a new blockchain

• I have read the guidelines for adding a new blockchain.