Add extending browser wait consideration for SSO auth to prerequisites

What does this MR do?

I have worked with 2 customers where they were caught out by the fact that DAST authentication was not waiting long enough for the page to load after SSO auth.

After setting DAST_BROWSER_ACTION_STABILITY_TIMEOUT, these customers were able to successfully get their DAST browser-based analyser working with SSO authentication so it is worth documenting.

There may be a better place to put this but I couldn't decide where so this is a first iteration. :-)

These settings (and more) are discussed in this internal issue with @cam_swords.

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