fix: image import for images with spaces in url

[preda-bogdan]

Summary

Fixed import for images from feeds where the image might contain encoded white space in the URL.
Added unit test to check for this case.

Will affect the visual aspect of the product

NO

Screenshots

Mapping example for import

Test instructions

1. Use this feed to test with: https://fetchrss.com/rss/64e0dbc093190f2b1a5d40b264e22cf23a76e05a277d6673.xml
2. Ensure [#item_image] is used inside the content and featured image from mapping. See the Screenshot example.
3. Check that all images are imported.

Check before Pull Request is ready:

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)

Closes #917.

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