Add build task to help DAST engineers setup the ZAP project

What does this MR do?

Helps a DAST user by downloading and building the ZAP Project. This is useful for engineers who want to understand more about how ZAP works, or for those who want to build a plugin to extend ZAP.

This MR adds the invoke task zap.setup-project. Executing the task will download the ZAP repository to ~/dev/zap or the folder specified by the environment variable ZAP_PROJECT_PATH. Gradle tasks are executed to build the zaproxy and zap-extensions project, and the built ZAP extension JAR files are copied into the zaproxy directory.

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Job definition example
  • Vendored CI Templates (also in CE)
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer