Add `rename` command

[geofflamrock]

Currently the only to rename a stack at the moment is to use the config file directly.

Add a new rename command which will change the name of a stack.

• Options:
  • --stack: The name of the stack to be renamed
  • --name: The new name of the stack
• The user should be prompted to select a stack if the --stack option is not provided.
• The user should be prompted to enter the new name if the --name option is not provided.
• Validate that there is not another stack with the same name for the same remote.

Technical notes

• Add any actions to the core domain Stack class as method e.g. ChangeName.
• Use existing helper methods for selecting a stack

Acceptance criteria

• New rename command added with required options.
• Unit tests added for command handling.
• Readme updated with details of the new command.