Integrate ZetaConnector with Gateway architecture (protocol v2)

[lumtis]

Describe the Issue

A v2 of the ZetaConnector was developed in https://github.com/zeta-chain/protocol-contracts but has been disabled for the time being.
This EPIC tracks the effort in order to enable the new ZetaConnector and consolidate all interactions around the gateway.

Tasks

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1. Pay gas fees in the contract for ZETA withdraws protocol-contracts#357
   priority:low +1
2. Implement depositAndRevert using ZETA tokens in addition to ZRC20 protocol-contracts#358
   priority:low +1
3. Support back ZETA for gateway protocol-contracts#394
   +0
4. Consider removing internalSendHash in ZetaConnector protocol-contracts#398
   +0
5. Add documentation for ZetaConnector deployment protocol-contracts#432
   docs +1
6. Support ZetaConnector V2 (gateway) #3213
   E2E m:crosschain m:fungible zetaclient +4
7. Write guide for ZetaConnector migration to v2 #3214
   docs +1
8. Track withdrawn ZETA #881
   zetacore +1