[py] Allow running the test suite with WPE WebDrivers and add a bazel target for it and GTK

[lauromoura]

Description

These changes allow using the WPE WebDriver to run the Selenium pytest suite.

Motivation and Context

The selenium test suite is imported into the WebKit to make it easier to run WebDriver (Selenium's and WPT's) tests against WebKit changes. Recently we enabled the tests for WPE build bots but only the WPT suite is actually being tested. The WPE webdriver is not listed in the conftest.py as one of the options to be tested.

Also, this request added bazel rules to make it easier to run both the GTK and WPE tests. Will these rules be automatically executed by CI? (Requiring a working WPE/GTK setup). If so, is there any way to make them optional?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
  • Covered by existing tests.
• All new and existing tests passed.
  • No changes in other browsers, some failures in the test suite with both GTK and WPE.

[CLAassistant]

All committers have signed the CLA.

[AutomatedTester]

merged by hand