Add graphql API to list Scan Execution Policies

What does this MR do?

This MR implements new GraphQL API to list Scan Execution Policies(scanExecutionPolicies): #329423 (closed)

Setup Scan Policies for a project

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 the policy project (security-orchestration-policies) that was created in step 1 and click save

Screenshots (strongly suggested)

When the project have configured security policy project with valid policy:

When an user who is not a developer or maintainer of the security policy project:

When the project does not have a configured security policy project:

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not 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.

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