Add modify_security_policy permission

What does this MR do and why?

Addresses #381714 (closed)

Currently we have read_security_orchestration_policies and update_security_orchestration_policy_project permissions, but they denote the ability to read/update the policy project associated to a target project. We are using the same permission to check if a user had permission to create/update a policy which is misleading. This MR introduces a new permission modify_security_policy that will be used to check if an user has access to create/update a security policy for a project/group.

graph TD
    A{Does Project A have Security Policy Project assigned?} -->|Yes| B{Does given user have Developer/Maintainer Permissions to Security Policy Project?}
    A{Does Project A have Security Policy Project assigned?} -->|No| C{Is given user an Owner of the Project A?}
    C{Is given user an Owner of the Project A?} -->|Yes| D(User can create/modify policies)
    C{Is given user an Owner of the Project A?} -->|No| E(User cannot create/modify policies)
    B{Does given user have Developer/Maintainer Permissions to Security Policy Project?} -->|Yes| F(User can create/modify policies)
    B{Does given user have Developer/Maintainer Permissions to Security Policy Project?} -->|No| G(User cannot create/modify policies)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create a security policy project for a development project from Security & Compliance -> Policies -> New Policy
2. Give a second user Maintainer Access to both the newly created Security Policy Project and the Development Project.
3. Log in as the second user and try to create or edit a security policy for the development project

MR acceptance checklist

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