Add 2-3 secured implementations for Persistent XSS

[preetkaran20]

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Is your feature request related to a problem? Please describe. As main target for Vulnerable App is scanners so we need to find out false positives by Scanners such that they can improve on there scan rules. So in order to find out the false positives, we need to add more secured implementations.

Describe the solution you'd like Add 2-3 more functions in https://github.com/SasanLabs/VulnerableApp/tree/master/src/main/java/org/sasanlabs/service/vulnerability/xss/persistent which are secure.