feat: custom script: skip step for authentication flow

[mmrraju]

Describe the issue

Here, is a test custom script, there have two case for completing the flow.
First case, it will flow step-1 > step-2 > steps-3 xhtml pages.
Second case it will flow step-1 > step-3 (skipping step-2) xhtml pages.
***First case is working but second case is not working ***

corresponding ticket is https://support.gluu.org/authentication/10977/skip-step-in-gluu-custom-script/

Expected behavior

authentication flow from step-1 to step-3 xhtml pages.

Actual behavior

Step-1 to showing error not step-3 xhtml page.

skipstep.zip

[yurem]

The issue that current flow allow to return back to specified step only. We need to support fast forward too

[yurem]

Implemented