Ignore negative index policies and rules for security policies

What does this MR do and why?

This MR fixes a bug from !163942 (merged) where if a policy is marked for deletion, the policy is still included in the diff comparison until the policy is fully deleted. The actual logic of deleting the approval rules is still in development (!163945 (closed)) and this fix is to make sure that we do not include deleted (to be deleted) policies for comparison.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

• Enable security_policies_sync and security_policies_sync_group feature flags
• Create a project and create a security policy for the project from Secure -> Policies
• After the policy is merged, verify that a row is created in security_polices table.
• Delete the policy and merge the MR to delete the policy. After the MR is merged, verify that the policy has negative policy_index
• From rails c, trigger Security::PersistSecurityPoliciesWorker again verify that the policy index is still negative

policy = Security::Policy.last
p policy.policy_index
Security::PersistSecurityPoliciesWorker.new.perform(policy.security_orchestration_policy_configuration_id)