Add section about custom device integration

[cappel89]

Add Learning material about status objects:

• CompareStatus, TransitionStatus, ExceptionStatus, AndStatus

Add how-to for status usage

• Add how-to use a status in a custom device integration (within PSIDeviceBase, without PSIDeviceBase)
• Add how-to for using Compare/TransitionStatus
• Add how-to combine status objects -> AndStatus
• Add how-to use an ExceptionStatus

[github-actions]

Remaining TODOs in the docs:

docs/how-to/devices/add-an-epics-motor.md:<!-- TODO: Add video here -->
docs/getting-started/quick-start/04-run-your-first-scan.md:<!-- TODO: link to learn about signals -->
docs/getting-started/quick-start/01-open-bec.md:<!-- TODO: link to different application modes. -->
docs/getting-started/quick-start/01-open-bec.md:<!-- TODO: link to information about deployments. -->
docs/getting-started/next-steps/script-gui-interactions.md:TODO: Revisit as a dedicated, safety-reviewed scripting tutorial.