[Swagger] The endpoint GET /categories/{id}/subjects doesn't correspond to the actual endpoint GET /categories/subjects/names.

[MilaKomisarenko]

Reproducible: always

Pre-conditions:

1. The site Space2Study is opened.
2. The user is logged in as a Tutor.
3. The "Edit profile" page => The "Professional info" tab is opened.

Steps to reproduce:

1. Click "Inspect" => "Network"
2. Click the "Add category" button.
3. Click "names" request.
4. Go to "Headers".
5. Go to "Response".
6. Go to https://s2s-back-stage.azurewebsites.net/api-docs/#/Categories/get_categories__id__subjects.

Actual result:

1. The endpoint -- /categories/{id}/subjects.
2. The response is

Expected result:

1. The endpoint -- /categories/subjects/names.
2. The response is