Adding Secure Implementation for PathTraversal Vulnerability

[preetkaran20]

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**Describe the enhancement ** Path Traversal Vulnerability doesn't have a secure implementation so we need to add the Secure implementation. This vulnerability, we need to also validate other levels for PathTraversal vulnerability that they are exploitable or not.

Glimpse of Path traversal vulnerability:

** How to Fix ** Add a new Level in https://github.com/SasanLabs/VulnerableApp/blob/master/src/main/java/org/sasanlabs/service/vulnerability/pathTraversal/PathTraversalVulnerability.java similar to how we added the other levels which has all the validations properly implemented. Adding Variant as secure to the annotation of the level which is VulnerableAppRequestMapping.