[docs] Create a better overview of TestCafe and its capabilities

[titerman]

What is your Scenario?

The Why TestCafe? article leaves a lot to be desired

What are you suggesting?

Split the article in two: Why TestCafe? and How does TestCafe work? Create a new article that goes over all the TestCafe capabilities

What alternatives have you considered?

No response

Additional context

No response

[helen-dikareva]

Related: https://github.com/DevExpress/testcafe-marketing/issues/313 https://github.com/DevExpress/testcafe-marketing/issues/316