Create SECURITY.md (#34956)

* Create SECURITY.md

* Simplified document

SECURITY.md was simplified to point to the VA Bugcrowd documentation and remove duplicate information.

* Updated SECURITY.md

Updated SECURITY.md to template agreed upon by Platform Security.

SECURITY.md

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+# Security Policy
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+The Department of Veterans Affairs participates in a Responsible Vulnerability Disclosure Program through Bugcrowd. Please report any security-related issues using our [Bugcrowd program](https://bugcrowd.com/va-vdp).
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+If your Bugcrowd submission is related to an open GH issue, please include that issue ID in the description field of your disclosure. 
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+But, please do not open new security-related issues. If you are a developer and have concerns, you can reach out on our internal Slack channel #platform-security.