Support ALLOW_VISUAL_REGRESSION_TO_FAIL flag

[JamesCatt]

The upstream cypress-visual-regression plugin that this is based on has a ALLOW_VISUAL_REGRESSION_TO_FAIL config flag to allow the Cypress tests to pass even if a diff over the threshold is detected, but it looks like this isn't supported on this fork.

Was hoping to make use of this feature. Happy to provide a PR if you'll accept one.

[Andremoniy]

hi @JamesCatt ,
Sure, feel free to provide a PR. Just don't forget to add tests.