Add headless browser to the WebSurferAgent

[vijaykramesh]

Why are these changes needed?

This adds a simple selenium driven headless browser to the WebSurferAgent. It does not yet make this headless browser agent multi-modal (e.g., it can't do anything with images in the browser) but this should work much better for javascript powered websites than the current SimpleTextBrowser implementation.

This also refactors the existing SImpleTextBrowser implementation a bit to have both share a common base class, and adds unit tests across both the existing and new HeadlessChromeBrowser implementation.

https://app.codecov.io/github/microsoft/autogen/pull/1534 shows the coverage additions there

Related issue number

Closes #1481

Checks

• [ ] I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• [x] I've added tests (if relevant) corresponding to the changes introduced in this PR.
• [x] I've made sure all auto checks have passed.