Implement Contract Admin Functionalities for storage contract

[sshubhamagg]

1. Implement fee management functions:

   function setRegistrationFee(uint256 _fee) external onlyOwner
   function setFeeCollector(address _collector) external onlyOwner
   

2. Implement registrar management:

   function addRegistrar(address _registrar) external onlyOwner
   function removeRegistrar(address _registrar) external onlyOwner
   

3. Implement pause functionality:

   function pause() external onlyOwner
   function unpause() external onlyOwner
   

Function Parameters:

setRegistrationFee:
- _fee: uint256 (amount in wei)

setFeeCollector:
- _collector: address (EOA wallet address)

addRegistrar:
- _registrar: address

Events Emitted:

RegistrarAdded(address indexed registrar, address indexed addedBy)
ContractPaused(address indexed by)
ContractUnpaused(address indexed by)

Events Emitted:

event RegistrationFeeUpdated(uint256 indexed oldFee, uint256 indexed newFee);
event FeeCollectorUpdated(address indexed oldCollector, address indexed newCollector);
event RegistrarAdded(address indexed registrar, address indexed addedBy);
event ContractPaused(address indexed by);
event ContractUnpaused(address indexed by);