Docs around scraping behind login

[B4nan]

quite common use case, but we dont have any guides around it in crawlee docs (and only sparse guides in the apify docs)

• use two crawlers, one browser for logins, one cheerio/jsdom for scraping, document how to do the interop between them (sharing cookies, pausing)

[barjin]

use two crawlers

Note: this is a topic on its own, because of #3024 and similar issues (e.g. running two AutoscaledPool instances).