[Medium] Add Credential Sharing contract

[Josie123-Dev]

Task Description

Create Credential Sharing contract:

• Share credentials securely
• Set sharing permissions
• Implement time-limited sharing
• Add sharing revocation
• Track sharing events

Requirements

• Sharing function
• Permission setting
• Time limits
• Revocation logic
• Event tracking

Acceptance Criteria

• Sharing works
• Permissions are set
• Time limits work
• Revocation works
• Events are tracked