Add the site_url() to the wp-json URL so directory installs work.

[donnchawp]

If a site is installed in a sub directory so that it doesn't live at "/" on the host, then feedback (and probably NPS) will fail because it sends wp-json requests to /wp-json/, not /sub-directory/wp-json/.

This patch fixes that by prefixing the wp-json path with the site_url().

To test:

1. Apply patch.
2. Run npm run build:apifetch.
3. That will update build/apifetch.js
4. Configure a WordPress install that is served off a directory, not "/", ie. https://example.com/test/ rather than https://example.com/
5. Install the Crowdsignal Forms plugin and connect it to Crowdsignal
6. copy build/apifetch.js and includes/frontend/class-crowdsignal-forms-blocks-assets.php into the wp-content/plugins/crowdsignal-forms/ directory, overwriting what was there.
7. Add a feedback button to a post and send feedback. Make sure it loaded from the right directory.

Also try posting feedback before updating those files and you should see a 404 error in the web network.

[DustinHartzler]

Looks good to me 🚢

Updated the built file and the PHP file and the feedback form is submitted both to email and to the Crowdsignal dashboard.