Missing feedback when no fleeting plugins to install

Summary

The GitLab Runner CLI does not provide an indication when fleeting plugins are not installed.

Expected Behaviour

The gitlab-runner fleeting install command will only install the plugins that are specified in the configuration file. However, if the configuration is misconfigured or if the user mistakenly runs the command before ensuring the necessary configuration exists, I expect that it at least inform me so:

$ gitlab-runner fleeting install
Runtime platform                                    arch=amd64 os=linux pid=48 revision=66a723c3 version=17.5.0
No plugins detected.

Actual Behaviour

At present, it provides no feedback to the user that no plugins were installed.

$ gitlab-runner fleeting install
Runtime platform                                    arch=amd64 os=linux pid=48 revision=66a723c3 version=17.5.0

Proposed Enhancements

I will propose that we at least emit a message to inform the user that there are no plugins to install as shown above.