Update the ModalAjaxController::hookModalSubmit() to return JSON instead of int value

I've been working on addressing the issue as described, and here's a summary of the changes I made:
- Updated ModalAjaxController::hookModalSubmit() to return a JSON response instead of integers: Instead of directly echoing TRUE or FALSE and exiting, I transitioned to using structured JSON responses. This approach provides more context on the outcome, whether it's a success or a failure, and offers additional information that can be helpful for debugging.

- Modified the Ajax code in modal-page.js to correctly handle and act upon the new JSON response format. Error messages are now logged to the console for debugging purposes.

Attached is the patch with the changes I've made. Feedback and further testing are appreciated!

Thanks for the patch @tguerineau, let's review the code and test it

It's working fine, just come points on phpcs

FILE: modal_page/src/Controller/ModalAjaxController.php
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FOUND 6 ERRORS AFFECTING 6 LINES
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 101 | ERROR | [x] Namespaced classes/interfaces/traits should be referenced with use statements
 104 | ERROR | [ ] The array declaration extends to column 85 (the limit is 80). The array content should be split up over multiple
     |       |     lines
 112 | ERROR | [ ] The array declaration extends to column 84 (the limit is 80). The array content should be split up over multiple
     |       |     lines
 118 | ERROR | [ ] The array declaration extends to column 108 (the limit is 80). The array content should be split up over multiple
     |       |     lines
 130 | ERROR | [x] Expected newline after closing brace
 136 | ERROR | [ ] The array declaration extends to column 115 (the limit is 80). The array content should be split up over multiple
     |       |     lines
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PHPCBF CAN FIX THE 2 MARKED SNIFF VIOLATIONS AUTOMATICALLY
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Time: 959ms; Memory: 14MB

Adjusted phpcs

Moved to the dev branch. Thank you so much for your great job @tguerineau

I think we can implement the same improvement on this other method to be consistent

Automatically closed - issue fixed for 2 weeks with no activity.