Add --gha option to sbase mkdir

[AtaSahin]

What changed

• Added --gha / --github-actions to sbase mkdir to generate a GitHub Actions workflow in the created project.
• Supports optional matrix flags (browsers / python / OS) with sensible defaults.

Why

• New SeleniumBase projects often need CI immediately. This removes boilerplate and makes it easy to run tests on push/PR with artifacts available for debugging.

Usage

• sbase mkdir ui_tests --gha
• (optional) sbase mkdir ui_tests --gha --gha-browsers=chrome,firefox --gha-python=3.11,3.12 --gha-os=ubuntu-latest

Notes

• Does not overwrite an existing workflow file. Errors clearly if it already exists.
• Can be combined with --basic and keeps existing mkdir output unchanged besides adding the workflow file.

[mdmintz]

I like the idea of adding a --gha option to sbase mkdir DIR, but I'm not a fan of the way it's implemented here.

There are several issues I have with this PR:

• You changed code that's unrelated to the goal.
  --> (Eg. Markdown * Examples replaced with - Examples)
  --> It's not a good idea to change the styling of someone else's project.
• You added tests that don't actually test that the GitHub Actions YML is valid and works.
  --> You added asserts for lines of code generated, which isn't that helpful.
  --> Instead, a link to a GitHub Actions job that ran your generated YML would've been more helpful.
• The YML file imports are using out-of-date versions:
  --> actions/checkout, actions/setup-python, actions/upload-artifact.
  --> This is a common issue with AI-generated code. (Always proofread anything AI-generated!)
• It's overcomplicating the goal of a boilerplate --gha option for sbase mkdir DIR.
  --> People can modify that file from there when they want to add customization options.
• The documentation and output hasn't been fully updated to reflect the new --gha option.
  --> Eg. The original sbase mkdir DIR displayed a file tree for files generated.
• Your YML file is using older Python versions like 3.10 and 3.11.
  --> Why not use the latest by default?
• Your YML file is only uploading artifacts on failure.
  --> It's possible to have artifacts on success too.
• Your code doesn't follow the style guide rules that have been set for this project.
  --> (Eg. flake8 linter rules.)

Also, the SeleniumBase/CONTRIBUTING.md ReadMe states that we don't accept PR contributions (with some special exceptions). It's mainly because it takes a long time to review a PR and provide feedback (like this), and because (as you can see) there's a very high standard set. It takes a great deal of experience in SeleniumBase before most people are knowledgeable enough to make serious contributions directly to the project. That's why it's a better idea to submit suggestions rather than trying to make the changes yourself.

The idea of a --gha option for sbase mkdir DIR is nice though, and therefore I've implemented it here: #4198.
I'll close this PR in favor of that.