Create SECURITY.md (#2367)

* Create SECURITY.md

Signed-off-by: Yusuke Kato <kpango@vdaas.org>

* style: format code with Gofumpt and Prettier

This commit fixes the style issues introduced in e8609b0 according to the output
from Gofumpt and Prettier.

Details: #2367

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Signed-off-by: Yusuke Kato <kpango@vdaas.org>
Co-authored-by: deepsource-autofix[bot] <62050782+deepsource-autofix[bot]@users.noreply.github.com>

SECURITY.md

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+# Security Policy
+
+## Supported Versions
+
+We currently offer security updates for the following Vald versions:
+
+| Version | Supported          |
+| ------- | ------------------ |
+| v1.7.x  | :white_check_mark: |
+| v1.6.x  | :white_check_mark: |
+| < v1.6  | :x:                |
+
+## Reporting a Vulnerability
+
+At Vald, we prioritize software security. If you discover a security vulnerability, please report it to vald@vdaas.org.
+
+When reporting a vulnerability, please provide:
+
+- A clear and concise description of the vulnerability.
+- Steps to reproduce the issue.
+- Any relevant versions or configurations to aid in diagnosing the problem.
+- Any potential solutions or mitigations you may know of.
+
+We will assess your report promptly and respond as soon as possible. Once we reply, we will keep you informed about the fix progress and a comprehensive announcement. We value your responsible disclosure and will recognize your contributions.
+
+## Security Update Policy
+
+Our goal is to address all reported security issues promptly. Upon confirming a security concern, we will promptly release patch updates for the two most recent Vald minor versions. We advise all users to apply security updates as soon as they become available.
+
+Thank you for contributing to the safety of Vald and its users.