Improve ergonomics of CLI arguments in examples

[Mallets]

At the moment, CLI arguments are passed to zenoh-c examples in a very primitive way where each argument is solely identified by its position. While this approach does the job to quickly test out zenoh-c examples, its ergonomic is very poor and should be improved.

Common CLI arguments parsing should be used: e.g., to be able to use short (-o) and long (--option) arguments. Moreover, a default --help argument should be added to show for any given examples what CLI arguments are available and how they can be used.

In order to keep zenoh-c and zenoh-pico examples aligned and interchangeable as much as possible, this issue is linked to the same zenoh-pico issue here.