Add Predicate-Based Behavior Tree Executor

[ajtudela]

This PR introduces a new predicate-based behavior tree executor (PredicateBTExecutor) for executing behavior trees, enabling sub-symbolic checks of predicates.

• The PredicateBTExecutor integrates with the WaitAtStartReq BT node and is responsible for checking if predicates exist using the ProblemClient and executing predicate-based behavior trees for sub-symbolic validation.
• New parameters have been added (predicate_plugins, predicates_bt_xml) similar to BT Actions to retrieve the names and XML templates of the behavior trees.
• These XML templates are passed to the PredicateBTExecutor through the Blackboard for seamless integration.

I have successfully tested this implementation on our robots and believe it's worth discussing for potential integration.

[fmrico]

Can you explain the advantages of this approach and the problem that this PR wants to fix? Also I need to see why to use a BT for checking predicates

[ajtudela]

The PR attempts to bridge the gap between symbolic and subsymbolic information by introducing a mechanism for verifying predicates using behaviour trees. Each predicate is linked to a BT node, and when the executor needs to check whether the symbolic predicates have been met, it also executes the associated BT.

[roveri-marco]

That's great! I was indeed planning to do something similar. Does it also work with numeric fluents? What's thei role with the effects of an action?

[ajtudela]

That's great! I was indeed planning to do something similar. Does it also work with numeric fluents? What's thei role with the effects of an action?

It is currently just a proof of concept, with only the at-start requirements implemented. I'm no expert on planning and I'm not exactly sure how the effect works.