PC-335 Fix image requests in elementor

[thijsoo]

Context

• This prepares our elementor integration for if ever tinymce changes the way the handle the content. If that happens we don't want to start loading every image.

Summary

This PR can be summarized in the following changelog entry:

• Changes the way the elementor data collection handles images

Relevant technical choices:

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• Add an image to a post and check if the Image Keyphrase assessment shows up
• Add an alt tag to the image and check if the Image Keyphrase assessment shows Images on this page have alt attributes, but you have not set your keyphrase. or another version of the assessment where alt tags are available

Relevant test scenarios

• [ ] Changes should be tested with the browser console open
• [ ] Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• [X] Changes should be tested on different editors (Block/Classic/Elementor/other)
• [ ] Changes should be tested on different browsers
• [ ] Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• [X] QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

UI changes

• [ ] This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Other environments

• [ ] This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.

Documentation

• [ ] I have written documentation for this change.

Quality assurance

• [X] I have tested this code to the best of my abilities
• [ ] I have added unit tests to verify the code works as intended
• [ ] If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• [ ] I have written this PR in accordance with my team's definition of done.

Fixes #

[KiOui]

ACC: ✅