Added Key Expiration and Key Rotation (new)

[Entity069]

Related Issue

Closes #16

Type of Change

• New Feature
• Bug Fix
• Code Refactor
• Documentation Update
• Other (please specify):

Description of Change

Implemented a feature for key expiration and key rotation.

Implementation Details

• Implemented two key expiration : Key creation date is stored in the second line of the key file
• Implemented key rotation : If key is expired (by default expiration date is 30 days), then user is provided with an option to regenerate key and re-encrypt all files password files.
• Added is_key_expired function to check if the key is expired
• Added rotate_key to regenerate the key and re-encrypt all password files
• Changed main.py to ask user for regeneration prompt and prompt for password files