add: --dry-run flag

[mieliespoor]

Specifying the --dry-run flag will perform all the steps except any permanent actions. This will then result in the cli collecting everything that it normally would and perform any Octopus API calls that would normally happen, except making any permanent changes.

This is very useful to run to allow you to test it out and see what the output would be without modifying anything within Octopus. In our CI pipeline we provide the option to specify a dry-run flag, but at this point in time we skip the steps where permanent changes will be made within Octopus as we don't have the option to pass the --dry-run flag to the cli.

octopus release create --dry-run
octopus release delete --dry-run
octopus account create --dry-run