Fixed #22266: 404 message for product alerts when not logged in

[ArjenMiedema]

Description (*)

When the user isn't logged in and presses the product alert link
(either stock or price), the user has to login and gets redirected
to a 404 page. This is because the redirect done by the login page
is a GET call. The fix done is to change the used interface for
the product alerts from POST to GET, as this is the easy fix and
there's no reason to use POST here at this moment, as all parameters
for the call are all in get URL parameters.

Fixed Issues (if relevant)

1. Product Alert after login shows 404 page #22266: Product Alert after login shows 404 page

Manual testing scenarios (*)

1. Create a product in the Magento backend and ensure it's not in stock
2. Make sure you enable stock and/or price alerts in the configuration and clean the config and full page cache
3. Go to the frontend of the webshop and ensure you're not logged in
4. Go to the newly created product
5. Click the stock alert link and/or the price alert link
6. Login or create an account here
7. Ensure the product is added to the stock/price alerts of the current customer account

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)

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[magento-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

Hi @dmytro-ch, thank you for the review.
ENGCOM-5267 has been created to process this Pull Request

[makkoff]

✔️ QA Passed

[ghost]

@magento-cicd2 unfortunately, only members of the maintainers team are allowed to unassign developers from the pull request

[m2-assistant]

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