[DAST] Add documentation for after-login-actions configuration

What does this MR do and why?

Adds documentation for the newly added --after-login-actions configuration available in DAST from V4.0.14

Related Issue: #427617 (closed)

Related Epic: &11585

Screenshots or screen recordings

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Before	After

How to set up and validate locally

• Turn on GitLab docs in the GDK and navigate to ee/user/application_security/dast/browser_based.html#available-cicd-variables

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #426505 (closed)