Improve API documentation: fix for demo server path, added `403` error responses, improved schema for paginated responses

[romalytvynenko]

This PR brings a few improvements to API docs.

1. By upgrading Scramble and Scramble PRO to 0.12.35 and 0.7.18, Cachet API docs will have a more accurate pagination information schema (links are optional, but when present – they'll be strings).

2. Fixed demo server path (was https://v3.cachethq.io but the correct one is https://v3.cachethq.io/api).

3. Added /** @throws MissingAbilityException */ annotation to the GuardsApiAbilities trait. This, in turn, improved documentation of endpoints that use this trait and now include a 403 response.

Altogether, this makes the documentation more accurate and consumers of this API happier 🫶