Move trigger logic to base Sensor class and enable trigger for all ca…

[shameekganguly]

…mera sensors

🦟 Bug fix

Fixes https://github.com/gazebosim/gz-sensors/issues/426

Summary

This PR ensures that when a camera sensor is triggered, it will publish a new image on the next update call. Additionally, if Update() is called with _force = true, data will be always generated irrespective of whether a trigger is pending or not. To do this, the following changes are made:

• Moved trigger logic to base Sensor class
• Added new Sensor class methods EnableTriggered, DisableTriggered and HasPendingTrigger
• Set all camera-type sensors to correctly enable triggered mode if it is specified in the SDF
• Update integration tests

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