Fix incorrect label async request paths

[joshuatf]

Fixes #1424 fixes #1425

Fixes the request paths for getting labels to prevent the 404 and also show persisted comparison labels on page reload.

Screenshots

Detailed test instructions:

1. Go to the products report.
2. Select 2 product using the product comparison filter and click "Compare."
3. Make sure no 404s are shown under network requests.
4. Refresh the page.
5. Make sure that the comparison tags persist after reloading.
6. Make sure that coupons, customers, and product variation comparison filters continue to work as expected.

[Aljullu]

Tested and it fixed both issues. Thanks for taking this @joshuatf!