Feature: History Tracking for Workflow Variable Mutations

### Summary:
Introduce the ability for Elsa 3 to maintain and track a history of workflow variable mutations.

### Background:
Elsa currently supports defining and using workflow variables, but once an activity modifies a variable, the previous state/value of the variable is lost. For debugging, audit, and data analysis purposes, it would be invaluable to have a traceable history of how a variable has changed over time throughout the workflow execution.

### Feature Description:
1. **History Object**: Whenever a workflow variable is mutated (e.g., updated, deleted), capture:
- The previous value of the variable
- The new value of the variable
- The timestamp of mutation
- The activity ID/name that initiated the mutation

2. **Accessible via API**: Expose an API endpoint that allows users to query the history of a variable by workflow instance or variable name.

3. **UI Integration**: In Elsa's dashboard, under each workflow instance, provide a section/tab dedicated to showcasing the history of variable mutations in a timeline or tabular format.

4. **Configurability**: Allow users to turn on/off this feature at the workflow or global level to cater to performance and storage considerations.

### Use Case:
Consider a workflow where variable `X` starts with the value `10`, is updated to `20` by `Activity A`, and then changed to `30` by `Activity B`. With this feature, a user can trace back the mutations, understanding which activity modified the variable and when.

### Potential Benefits:
- Enhanced debugging: Easily trace back the sources of unexpected variable values.
- Auditing: Maintain a clear record of how data changes throughout the workflow execution.
- Data Analysis: Analyze patterns of data mutations for insights and improvements.

Would love to hear thoughts on the feasibility, and any additional requirements or concerns associated with implementing this feature.