Image CDN should be aware of different doc versions

Describe the bug
Currently, changing the version of the document does not load images from specific branch.
i.e. all versions share the same image source from CDN https://download.pingcap.com

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
For each version maintained, have corresponding CDN path that stores the images from their branch
Take docs v5.2 as example:

• media dir https://github.com/pingcap/docs/tree/release-5.2/media
• CDN path: https://download.pingcap.com/v5.2/

Screenshots

• dev
  

• v5.2
  

The src of the image is always the same

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Related code: https://github.com/pingcap/website-docs/blob/e612ad0095cea2c2e40d179d80eb3df253bf7ea1/packages/download/utils.js#L17

Start at packages/download/utils.js around line 17 and compare how the selected document version determines its image source. Verify the release-5.2 example against the media directory and CDN path; done means each maintained version resolves images from its corresponding versioned CDN location.