feat: Make Contracts Upgradeable

[tesol2y090]

Description

This PR modifies contracts to support upgradeability using OpenZeppelin's upgradeable contracts pattern. This change allows for future upgrades while preserving the contract's state and functionality.

Changes

• Added Initializable contract from OpenZeppelin's upgradeable contracts
• Implemented constructor with _disableInitializers() to prevent initialization of the implementation contract
• Added initialize() function to replace constructor functionality
• Maintained existing public state variables and functions
• Modified AxelarExecutable.sol to be upgradeable:
  • Added OpenZeppelin's Initializable contract
  • Replaced constructor with initializer function
  • Made state variables mutable for upgrades
  • Added proper initialization pattern

Related Issues

• Upgradable smart contracts #22

[longfeiWan9]

@tesol2y090 sorry, I did not see this PR. I will review it