Adds Habitica calendars

[tr4nt0r]

Proposed change

Adds calendar as platform for Habitica and description for the calendar entities

Type of change

• [ ] Spelling, grammar or other readability improvements (current branch).
• [ ] Adjusted missing or incorrect information in the current documentation (current branch).
• [ ] Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • [ ] I've opened up a PR to add logos and icons in Brands repository.
• [x] Added documentation for a new feature I'm adding to Home Assistant (next branch).
• [ ] Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase: https://github.com/home-assistant/core/pull/128248
• Link to parent pull request in the Brands repository:
• This PR fixes or closes issue: fixes #

Checklist

• [x] This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• [x] The documentation follows the Home Assistant documentation standards.

Summary by CodeRabbit

• New Features
  • Introduced a "Calendar" category to the Habitica integration, enhancing task management capabilities.
  • Added a new section detailing "To-Do calendar" and "Dailies calendar" functionalities for better tracking of tasks and routines.