[POC] Handle config deprecation and migration in connectors-sdk

[throuxel]

Proposed changes

This PR introduces a deprecation handling system for the connectors SDK, managing automatically different use-cases while maintaining backward compatibility.

• LegacyField(): Mark fields as deprecated with migration metadata
• DeprecatedNameSpace & DeprecatedVariable: Annotated types for deprecated configurations
• Automatic migration via migrate_deprecation() validator in BaseConnectorSettings
• Support for variable renaming, namespace migration, and value transformation
• User-friendly deprecation warnings

Exemple:

class MyConfig(BaseConfigModel):
   old_var: DeprecatedVariable = LegacyField(
       deprecated="Use new_var instead",
       new_variable_name="new_var",
       change_value=lambda x: x * 60  # Optional transformation
   )
   new_var: int = Field(description="New variable")

class ConnectorSettings(BaseConnectorSettings):
   old_namespace: DeprecatedNameSpace = LegacyField(
       deprecated="Use new_namespace instead",
       new_namespace="new_namespace"
   )
   new_namespace: MyConfig = Field(default_factory=MyConfig)

Related issues

Checklist

• I consider the submitted work as finished
• I have signed my commits using GPG key.
• I tested the code for its functionality using different use cases
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

The dummy connector is only for demo, and should be removed before merging.