Update security policies pipeline processor to support secret detection

What does this MR do?

Addresses #334415 (closed)

We want Secret Detection scans to be run whenever a project pipeline is run according to the policy mentioned in the security policy project. Secret Detection scans should run in normal mode for pipeline. Normal mode is typically enabled by setting SECRET_DETECTION_HISTORIC_SCAN to false as a CI variable. (See documentation)

How to setup and validate locally (strongly suggested)

Feature documentation: https://docs.gitlab.com/ee/user/application_security/policies/

1. Clone and create a project from https://gitlab.com/sashi_kumar/security-orchestration-policies
2. Enable security_orchestration_policies_configuration for the target project for which the scan policies should be enabled for by doing:

Feature.enable(:security_orchestration_policies_configuration, Project.find(<target_project.id>))

1. Go to Security & Compliance -> Scan Policies for the target project
2. Select Edit policy project and select the policy project (security-orchestration-policies) that was created in step 1 and click save
3. Create a new pipeline and notice that secret-detection-0 job is included under test stage.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• 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