Closes #140: Isolate VR Tests to be generic for all WPR features

[jeawhanlee]

Description

Fixes #140
Allows Visual Regression tests to be run against any WPR feature.

Type of change

• New feature (non-breaking change which adds functionality).
• Enhancement (non-breaking change which improves an existing functionality).

Detailed scenario

N/A

Technical description

Documentation

Visual Regression tests can now be run against any WPR feature by just running:
npm run test:vr --wproption=rucss where rucss is a recognized option in the testsuite, full reference of options that can be parsed are found here: https://github.com/wp-media/wp-rocket-e2e/blob/8e61ff1f734b8784aa2198f6fb2b96aa3ca2cf3f/src/common/selectors.ts

New dependencies

N/A

Risks

N/A

Mandatory Checklist

Code validation

• I validated all the Acceptance Criteria. If possible, provide screenshots or videos.
• I triggered all changed lines of code at least once without new errors/warnings/notices.
• I implemented built-in tests to cover the new/changed code.

Code style

• I wrote a self-explanatory code about what it does.
• I protected entry points against unexpected inputs.
• I did not introduce unnecessary complexity.
• Output messages (errors, notices, logs) are explicit enough for users to understand the issue and are actionnable.

Unticked items justification

• No built-in test to implement
• No entry points to protect

[Mai-Saad]

• checked PR with new cmd i.e npm run test:vr --wproption=lazyloadCssBgImg
• check PR with old suit having VR i.e npm run test:llcssbg
• Both are woking , noting that at backstop , some templates may fail (templates will be revisited in separate GH)
  
  

[Mai-Saad]

smoke test