Make the rule application consult the overall setting kill switch

Problem/Motivation

Currently the setting of "Validate alt text on save" is not being used. If this is switched "on" the validation should not happen.

Steps to reproduce

Proposed resolution

Dependency inject the module settings into src/Plugin/Validation/Constraint/AltTextRulesConstraintValidator.php
and skip all validation is the setting is turned off.

The report should be unaffected by this.

Remaining tasks

User interface changes

API changes

Data model changes