🐛 Support incident selectors.

[jortel]

Add support for incident selectors. Users can filter in/out incidents based on packages. The package is reported as an Incident.Variables with key=package.
The !package and !(package) syntax is used to match incidents without the package variable.

Passes --incident-selector option as needed.

Test cases and expected selector:

Case	Selector
Empty
Included (only)	(!package||package=a||package=b)
Included and Excluded	(!package||package=a||package=b) && !(package=C||package=D)
Excluded (only)	!(package||package=C||package=D)

[mansam]

LGTM