[ Feat ]: Revoke rights for a certain user

[brf153]

closes #79

Steps I have taken:

1. Created a new command to revoke user rights.
2. Implemented the /whiteboard deny {userName} of {boardName} command for this purpose.
3. Extracted userName and boardName from the context parameters.
4. Developed a new function to remove the specified userName from the boardOwner of the given board.
5. Updated the board using the storeBoardData function.
6. Sent a message to the board owner, notifying them that {userName} has been removed from the rights of {boardName}.