[API] Add stop upgrade endpoint

[mirkoCrobu]

Motivation

closes https://github.com/bcmi-labs/orchestrator/issues/382

Change description

Adding API endpoint PUT /v1/system/update/stop.
It stops service and platform updates.

The update cancellation is implemented via a SIGTERM signal (context cancellation) to allow for a graceful shutdown.

apt-get, In some phases, traps this signal to complete its current critical operation before exiting, delaying the interruption.

Additional Notes

Test

• Installing orchestrator with new features
• Start listening to events
  curl -X GET localhost:8800/v1/system/update/events
• Start updates
  curl -X PUT localhost:8800/v1/system/update/apply
• After 0,5 -1-3 seconds, stop updates
  curl -X PUT localhost:8800/v1/system/update/stop

Reviewer checklist

• PR addresses a single concern.
• PR title and description are properly filled.
• Changes will be merged in main.
• Changes are covered by tests.
• Logging is meaningful in case of troubleshooting.

[lucarin91]

@mirkoCrobu can you fix the conflicts?