Allow image src without scheme and with external domain

[fabienheureux]

Description

If images have a src attribute like //example.com/image.jpg, the imported url does not care about the domain and prepend the wagtail domain, hence leading to a 404 when downloading the image

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• Testing
  • [x] CI passes
  • [x] If necessary, tests are added for new or fixed behaviour
  • [x] These changes do not reduce test coverage
• Documentation.
  • [x] Documentation changes are not necessary because they do not change how the importer usage

[fabienheureux]

Sorry for the noise, I pushed without running tests locally, again :roll_eyes:, they now pass.

@nickmoreton do you think you could take a look ? I am not very proud of this approach, especially the hardcoded file extensions, but I did not see how could we better handle these various cases.

[nickmoreton]

@fabienheureux Thanks we really appreciate the pull request.

@nimasmi I tested it out and is working OK. Would you take a look please and confirm happy to merge. Thanks

[fabienheureux]

@nickmoreton I am cleaning up old PRs.

Can I close this one ?

I hope I could have take @nimasmi comment into account but never found the time and I won't use this plugin in a near future.