Add empty job assistant drawer on CI editor page

What does this MR do and why?

This MR is splitt from !105538 (closed) , it's the initial part job of #373382

design: #373382 (comment 1168364861)

Screenshots or screen recordings

QQ20221227-221848-HD

How to set up and validate locally

1. Enable the feature flag

   Feature.enable(:ci_job_assistant_drawer)

2. Visit any CI editor pages such as http://127.0.0.1:3000/root/demo/-/ci/editor?branch_name=master
3. Click the job assistant button.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

@daveliu @orozot @JeremyWuuuuu