feat: adds task notifcations window config settings

[jonathanbataire]

Description

• Adds task_notification_window object with start and end fields used to set when android should start and stop showing during the day
  fixes: Fire notifications during times when CHW is working cht-android#433

Code review items

• Readable: Concise, well named, follows the style guide, documented if necessary.
• Documented: Configuration and user documentation on cht-docs
• Tested: Unit and/or integration tests where appropriate
• Backwards compatible: Works with existing data and configuration. Any breaking changes documented in the release notes.

License

The software is provided under AGPL-3.0. Contributions to this project are accepted under the same license.