Enhance list-checks command

[ernilambar]

Refactor list-checks command with improvements.

• Fix: get_checks() of Default_Check_Repository by default does not return experimental checks. This PR fix that issue for returing all checks with parameter Default_Check_Repository::TYPE_ALL | Default_Check_Repository::INCLUDE_EXPERIMENTAL.
• Addition: --categories argument is added to filter checks by categories.
• Addition: --stability argument is added to filter checks by stability. Takes either stable or experimental.

Output:

wp plugin list-checks --stability=stable - Currently all checks will be displayed as we dont have experimental checks yet.

wp plugin list-checks --categories=performance

wp plugin list-checks --categories=performance,general

[ernilambar]

cc: @swissspidy @felixarntz @mukeshpanchal27

[ernilambar]

Updates:

• get_checks() will return stable checks only by default. If --include-experimental is given, it will include experimental checks along with stable checks.
• --categories - Existing Check_Categories::filter_checks_by_categories() is used for filtering checks based on categories.
• --stability is removed and implemented --include-experimental flag.

[swissspidy]

Those Behat failures are unrelated and fixed in #381