[Docs]: improve "Setting up CI"

[t1]

Page(s)

https://playwright.dev/java/docs/ci-intro

Description

I think there are two details that could be improved:

• In the Introduction, the "detailed doc on Continuous Integration" could link to https://playwright.dev/java/docs/ci
• The suggested mvn exec:java doesn't work if the Playwright dependency is only test scoped. To fix that, one could add a -Dexec.classpathScope=test parameter.

[yury-s]

Feel free to send a PR to update the docs, they leave under https://github.com/microsoft/playwright/tree/main/docs/src