## Summary
This PR is a follow-on from Charlie's two branches, one for agents and one for actions. This list of changes describes work done by both Charlie and myself
- Agents are now extensible
- Refactored observation manager, action manager, and reward function to inherit from BaseModel
- Added a config schema to observation manager, action manager, and reward function
- Streamlined the way agents are created from config
- Agent config no longer requires a dummy action space if the action space is empty, the same applies for observation space and reward function
- Actions are now extensible
- Actions now support a config schema, to allow yaml data validation and default parameter values
- Action parameters are no longer defined through IDs, instead meaningful data is expected directly in the action map
- Test and example YAMLs have been updated to match the new agent and action schemas, such as:
- Removed empty action spaces, observation spaces, or reward spaces for agent which didn't use them
- Relabeled action parameters to match the new action config schemas, and updated the values to no longer rely on indices
- Removed action space options which were previously used for assigning meaning to action space IDs
- Updated tests that don't use YAMLs to still use the new action and agent schemas
- I haven't checked the notebooks run and there's a couple places where find-and-replace issues persist. I will fix but we can start review in the meantime if you're bored
## Test process
unit test
## Checklist
- [X] PR is linked to a **work item**
- [ ] **acceptance criteria** of linked ticket are met
- [X] performed **self-review** of the code
- [X] written **tests** for any new functionality added with this PR
- [ ] updated the **documentation** if this PR changes or adds functionality
- [ ] written/updated **design docs** if this PR implements new functionality
- [X] updated the **change log**
- [X] ran **pre-commit** checks for code style
- [ ] attended to any **TO-DOs** left in the code
Related work items: #2869, #2912
## Summary
These changes align core software with the approach that support extensions.
## Test process
Passes test suite.
## Checklist
- [X] PR is linked to a **work item**
- [X] **acceptance criteria** of linked ticket are met
- [X] performed **self-review** of the code
- [X] written **tests** for any new functionality added with this PR
- [ ] updated the **documentation** if this PR changes or adds functionality
- [ ] written/updated **design docs** if this PR implements new functionality
- [ ] updated the **change log**
- [X] ran **pre-commit** checks for code style
- [ ] attended to any **TO-DOs** left in the code
Related work items: #2888
