Write the security policy and set up policy reporting on all kpt repositories

[liamfallon]

Currently we have a security policy on the Porch repo (inherited from Nephio). There is no security policy on any of the other kpt repos.

Security vulnerability reporting was already turned on for the porch and kpt-backstae-plugins repos, it is now turned on for all kpt repos.

For security, the following actions should be undertaken:

1. Revise the Porch security policy to incorporate github security vulnerability reporting
2. Copy the Porch security policy to all kpt repos
3. Enable the following settings on all non-admin kpt repos (Under Security and quality)

• Security policy
• Security advisories
• Private vulnerability reporting
• Dependabot alerts
• Code scanning alerts
• Secret scanning alerts

4. Monitoring of security alerts should be a standing item on the weekly technical meeting