docs: Avoid third-party with Network API
On the [Avoid testing third-party
dependencies](https://playwright.dev/docs/best-practices#avoid-testing-third-party-dependencies).
Instead of only inform about third-party, this sesison is a good place
to share about Network API. Guiding them in not only inform about
avoiding third-party, but also explaining how to deal with this use
case.
Signed-off-by: Jonatas Emidio <jonatasemidio@gmail.com>
