Add support to crashd_config to declare required local programs

[vladimirvivien]

As a script developer, I should be able to specify required program used in the script. If the program is not found or not installed, the script should fail fast. Example:

crashd_config(requires=["docker", "ssh"])

In the previous snippet, if program docker and ssh are not found on the local machine's execution path, the script should fail.