feat(examples-plugins): add package-json plugin 📦

[BioPhoton]

This PR includes:

• docs
• logic
• unit-tests
• integration-tests

Additional changes:

• adopted scoring logic. the scoring logic returned NaN for some cases. Now it throws for empty refs
• adopted validation of CategoryConfig. Now it throws for empty refs
• adopt validators of CategoryRef. Now min length 1
• adopted plugin-eslint exports

[BioPhoton]

@matejchalk the currently failing 'CI / Code PushUp (push) ' job may be due to server bug in scoring logic. I DMed you.

[vmasek]

@BioPhoton did the discussion we had on "it's 100 not 0" yesterday help to unblock the failing problem or is it still a blocker?
I like this plugin as is and consider using it for some of the categories in projects we will be soon connecting

[BioPhoton]

Well I guess it is also a change for the backend no?

[matejchalk]

Well I guess it is also a change for the backend no?

Maybe, depends on what the agreement is. Our last chat was inconclusive.

• If we don't want to support categories with all refs of weight 0, then changing the backend is not required (although the error message could be improved), instead this plugin should fix it (e.g. change weights from 0 to 1).
• If we want to add an exception for such categories and give them a score of 0 or 1, then it needs to be changed both on the CLI and the BE.

[BioPhoton]

added a weight for now

[BioPhoton]

@matejchalk I implemented a solution for "empty" category refs.

It will get validated by the model now and throws in both cases. the schema and the scoring logic.

How should we deal with groups? Here I'm not sure.

[BioPhoton]

@matejchalk I resolved all comments. Thanks a lot for the review. I also added more tests for the type property.

Last thing would be this: #354 (comment)