CCM-12616 mesh poll retrieve

[lapenna-bjss]

Description

This PR introduces two components that together implement the full workflow for pulling and downloading requests submitted to the MESH mailbox.

The first component, mesh-poll, runs every five minutes, reads messages from the MESH inbox, extracts metadata from the message headers, including meshMessageId and messageReference (the MESH local_id), validates the sender by comparing the message’s mailbox ID against sender configurations stored in SSM, and resolves the corresponding senderId. Once validated, mesh-poll publishes a MeshInboxMessageReceived CloudEvent containing senderId, meshMessageId, and messageReference.

The second component, mesh-download, consumes these events via SQS, retrieves the MESH message using the meshMessageId, stores the document in the PII S3 bucket under the document-reference/{senderId}_{messageReference} key, acknowledges the message in MESH (removing it from the inbox), and finally publishes a MeshInboxMessageDownloaded CloudEvent.

Note:
In development environments, the pipeline uses mock MESH

Test evidence added in the Jira ticket comments

Utils Added

• event-publisher-py: Python implementation of the EventPublisher (mirrors the TypeScript version).
• Pydantic CloudEvent Models: Pydantic schemas used to validate all inbound and outbound CloudEvents (MeshInboxMessageReceived, MeshInboxMessageDownloaded).
• metric-publishers
• PyMockMesh: Mock implementation of the MESH client used in tests.

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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Sensitive Information Declaration

To ensure the utmost confidentiality and protect your and others privacy, we kindly ask you to NOT including PII (Personal Identifiable Information) / PID (Personal Identifiable Data) or any other sensitive data in this PR (Pull Request) and the codebase changes. We will remove any PR that do contain any sensitive information. We really appreciate your cooperation in this matter.

• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.