Enable addon previews (screenshots) to be added/deleted via the addon api

[eviljeff]

split from #8516

We want to be able to add and remove (and edit) the addon previews/screenshots via the api, like we can in devhub. Because there can be many we'll likley want a sub-endpoint under addon dedicated to creating, listing, deleting, etc, the previews.

[ioanarusiczki]

@eviljeff Could you add some details about this?

I did not find instructions in the docs about previews so I tried attaching a .jpg to "preview" as form-data (same way as for icon) but it does not seem to work.

[ioanarusiczki]

@eviljeff found something here https://github.com/mozilla/addons-server/pull/19091/files#diff-c2b741fadc1162d0339214429b8efe1e6827c92fff032fa5d7068af81b9bbd71

[eviljeff]

@ioanarusiczki because there are multiple screenshots there's a separate (sub) endpoint:
https://addons-server.readthedocs.io/en/latest/topics/api/addons.html#preview-create

[ioanarusiczki]

@eviljeff
I verified POST, PATCH and DELETE on -dev for extensions and it looks good:

• I could add previews, edit and delete them.
• I get 400 responses (as expected) for a couple of situations:
  "Images cannot be animated."
  "Images must be smaller than 4MB"
  "Images must be either PNG or JPG."
  "Upload a valid image. The file you uploaded was either not an image or a corrupted image."

I ran into a situation: after I tried PATCH and DELETE on a theme id -> I get no response, Status and Time are blank.
POST create preview is returning status created but sending a preview for a theme has no impact in dev hub.
I replaced the id of the theme with an extension after this but I still get no response for PATCH and DELETE so I made new requests (into a new tab) which will work as expected.
Maybe the attempt to send a preview for a theme should throw an error ?

PATCH/DELETE after using a theme id/guid:

[eviljeff]

@ioanarusiczki yeah, I think it's better they throw an error rather than silently fail (or appear to succeed but don't show up in devhub because a different type of object has been created that gets ignored). Can you file a follow-up?

[ioanarusiczki]

@eviljeff
Yes, sure. #8756