[Website] Create a visual regression test suite

[noomorph]

Description

• [x] Set up a test suite in the website/ project using Percy.io.
• [x] Create a corresponding step in .github/workflows/website.html

We could start from a simple set of test pages:

• home page
• documentation (demo page)
• blog page
• showcase page

Reportedly, the easiest way to start is Percy Snapshots:

https://docs.percy.io/docs/percy-snapshot

You can see a similar use case here:

• https://github.com/rohit-gohri/redocusaurus/tree/main/website
• https://github.com/rohit-gohri/redocusaurus/blob/main/website/package.json#L22
• https://github.com/rohit-gohri/redocusaurus/blob/main/website/snapshots.js

Although, I'd advise sticking with snapshots.yml (YAML format) just like the docs say.

[noomorph]

@moutro, so what is left now is to create a GitHub actions step for that. Please make it conditional, e.g., by using this advice. The condition would be: if there are changes in website/src/css files, run the regression test step (percy ...).

[moutro]

@moutro, so what is left now is to create a GitHub actions step for that. Please make it conditional, e.g., by using this advice. The condition would be: if there are changes in website/src/css files, run the regression test step (percy ...).

Thanks for the doc and instructions. Created a GH Actions step - see PR#3866 linked here for review.