Add secret_detection to security_orchestration_policy JSON schema

What does this MR do?

Addresses #334418 (closed)

Adds secret_detection to one of the scan types in security_orchestration_policy JSON schema. secret_detection does not need any other fields, so site_profile and scanner_profile which are used by dast are not needed for secret_detection. They are ignored by using maxProperties property.

NOTE: Documentation is not updated now because the functionality is still not implemented and it will be added in #334417 (closed)

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team