[Docs] Develop and improve on-call schedules content

[alyssawada]

Develop a dedicated section for schedule-related content

• Improve discoverability of on-call schedule docs

• Separate content into task-based topics that support a specific user goal

• Add new topics to fill gaps in the user journey and increase the value of the scheduling-related docs

• [x] Develop section structure and IA

• [x] Draft Manage on-call schedules section landing page

• [x] Map existing content to new topics

• [x] Develop Create on-call schedule topic

• [x] Refactor and update shift swap content

• [ ] Draft schedule examples with at least two common schedules

Refer to FY25Q1 refactor doc for more details