CCM-12896: Generate Python Models

[gareth-allan]

Description

This PR adds a new application in src/python-schema-generator that takes the JSON event schemas built from the docs/src/cloudevents directories and produces Pydantic V2 model classes for each event (using datamodel-code-generator).

The Python model classes are generated in the existing src/digital-letters-events package, so that using them from Python uses the same package name as when using the Typescript types. Note that in order to be able to generate Pydantic classes from our schemas I have add to add a pre-generation step which uses the json-schema-merge-allof package to merge the allOf entries in the schemas, as datamodel-code-generator was otherwise producing empty classes to represent string fields that used an allOf property.

Context

This change means that we will now always have Pydantic model classes for each event that we have a schema defined for in the digital letters domain, and that any changes to the event schemas will automatically result in updated code.

Validation

Made some example changes to convert the mesh-poll lambda to Python and have it validate incoming data using the generated models: feature/CCM-12896_generate_python_models...test/CCM-12896_demo_pydantic_usage#diff-8a1058fb005c5dc6646f1c7f79d30ef5e549d0122909d209b88c0a375ddfc6f1

My nhs-notify-digital-letters directory before running make config:

My nhs-notify-digital-letters directory after running make config:

Compared the runtime of the workflow for this branch:

Against a branch taken from main:

We can see that the build times are largely unchanged.

Dev Container

To verify the changes work in the dev container.

Ran make clean outside of a container and verified there were no generated files in src/digital-letters-events/digital_letters_events:

Then reopened the workspace in a new Notify Loaded 1.0.17 dev container and verified the files had been generated (make config is run as part of the post-create command for the dev container:

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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