Add developers and maintainers to security policy project

What does this MR do?

Addresses #336523 (closed)

Currently, when creating a security policy project via the GraphQL mutation securityPolicyProjectCreate , only maintainers from the target project are added as developers in the newly created security policy project. As per requirements, developers and maintainers from the target project should be added as developers in the newly created security policy project.

Screenshots or Screencasts (strongly suggested)

Members in target project

Members in policy project

How to setup and validate locally (strongly suggested)

1. Enable feature flag

   Feature.enable(:security_orchestration_policies_configuration, target_project)

2. Add developers and maintainers to the target project
3. In graphql console post this mutation:

    mutation createPolicyProject{
      securityPolicyProjectCreate(input:{
        projectPath: <target_project_path>
      }) {
        project {
          id
          name
          repository {
            rootRef
          }
        }
        errors
      }
    }

4. Check if the added users are configured as developers in the newly created policy project.

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