Implement cluster app schema requirement 5 - "Properties should have descriptions"

[mogottsch]

What does this PR do?

This PR adds a new rule to the cluster-app rule set, which checks whether all properties have a title. The requirement for this rule is defined in this RFC.

In addition:

• Improves the output format of the verify command
• Refactors the file/package structure

What is the effect of this change to users?

schemalint verify PATH --rule-set cluster-app

The command will check if every property has a description. If not the property will be printed out.
The verification will not fail, as this rule is not a requirement (MUST), but only a recommendation (SHOULD).

How does it look like?

Any background context you can provide?

• RFC

What is needed from the reviewers?

You can test these changes, with the following command.

go run ./main.go verify ./pkg/lint/rulesmeta/rules/testdata/8_missing_titles_and_descriptions.json --rule-set cluster-app`

Do the docs/README need to be updated?

No.

Should this change be mentioned in the release notes?

• CHANGELOG.md has been updated

[marians]

Approving on the basis of the screenshot. Looks good!