chore: refactor using a unique symbol per token

[JDawg287]

Description

This PR prevents users from deploying tokens with the same symbols.

Behaviour before:

• The same user cannot deploy multiple tokens with the same symbol
• Different users can deploy tokens with the same symbol

Behaviour after:

• The same user cannot deploy multiple tokens with the same symbol
• Different users cannot deploy tokens with the same symbol

Fixes TP-781

Breaking changes

• Changes the TokenSent event to emit the token symbol along with the token address
• The following changes were made to some external functions of the ERC20Messaging contract, as tokens are now referred to by their symbols:
  • sendToken(SubnetId targetSubnetId, address tokenAddress -> sendToken(SubnetId targetSubnetId, string calldata symbol
  • getTokenByAddress(address tokenAddress) -> getTokenBySymbol(string calldata symbol)
  • tokenDailyMintAmount(address tokenAddress) -> tokenDailyMintAmount(string memory symbol)
  • tokenDailyMintLimit(address tokenAddress) -> tokenDailyMintLimit(string memory symbol)

PR Checklist:

• I have performed a self-review of my code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works