Implement the help command

There is an initial implementation to display the help for the rover --clone. This issue extends the implementation to the other commands available

Proposed approach:

rover --help to display all commands available
rover --clone --help to display the clone command
rover --landingzone -h or rover -lz --help to display the landingzone help command

When an a value is missing for a given attribute the rover displays the example and the detailed explanation of the attribute.
For example rover --clone-branch requires to set the name of the branch. The rover will fails and display the examples and the detailed explanation of the --clone-branch

Start with the existing rover --clone help implementation and inspect the entry points for the other commands named in the issue. Run the documented rover --help, rover --clone --help, and rover --landingzone -h or rover -lz --help flows. Done means each command shows the requested help, and missing values show their examples and detailed explanations.

Written by the indexing model from the issue text.