Add PoC exploit for CVE-2017-5638

[postmodern]

Add a PoC exploit for CVE-2017-5638,

Reference PoCs

• https://gitlab.com/luispereira2024/struts2-rce (also contains Dockerfile)
• https://github.com/FredBrave/CVE-2017-5638-ApacheStruts2.3.5/blob/main/CVE-2017-5638ApacheStruts.py
• https://github.com/mritunjay-k/CVE-2017-5638/blob/master/exploit.py

Vuln App

• https://github.com/vulhub/vulhub/tree/639e32be6c0425b11d7d56594761c5e599a6a9d5/struts2/s2-045
• https://gitlab.com/luispereira2024/struts2-rce

How to Submit a PoC

See the CONTRIBUTING file for instructions on how to submit a PoC exploit.