Add default_selector and improve documentation on host labels and selection

[marvinhinz]

• [ ] Bug fix #…?
• [x] New feature #3198
• [ ] BC breaks?
• [ ] Tests added?
• [x] Docs added?

The default_selector was pretty quick to implement. I also added some documentation.

Would like to get some feedback on this!

congrats on the v7 release 🔥

[joelpittet]

This looks pretty solid solution @marvinhinz 👏

[joelpittet]

The documentation updates are a great touch too. Maybe could be shorter but they do describe the flexibility

[marvinhinz]

Thanks! In the meantime i thought about another comfort feature. In addition to a default_selector, we could use selector maps or aliases. I'm a fan easy to remember commands, so for a big project setup with many servers a deployment to production can be a bit complicated as you might need to enter something like dep deploy stage=prod&role=web,role=special everytime.

add('selector_map', [
    "prod" => "stage=prod&role=web,role=special",
    "staging" => "stage=staging",
]);

could then result in:

dep deploy prod

@antonmedv whats you opinion on this?

[marvinhinz]

@antonmedv seems like in the meantime you added documentation about the selectors itself, would you consider the default_selector functionality to be merged when i update this pr to the new documentation?