VED-981 Add base infrastructure for the MNS Publisher feature

[dlzhry2nhs]

Summary

• Routine Change

Simple architecture change to enable coding work to begin on the Lambda. Details of the ticket are no longer relevant, so will update in JIRA. Discussed with architect who was happy with the changes.

• Adds a stream to the delta table
• Adds a new MNS Publisher Lambda function which will read from the new delta stream

This approach minimises the number of new components we will need while ensuring that we are only publishing MNS events where the event was successfully persisted across the whole system i.e. the events table and delta.

Have raised a couple of questions, which I'm happy to look into under this PR or

Reviews Required

• Dev

Review Checklist

ℹ️ This section is to be filled in by the reviewer.

• I have reviewed the changes in this PR and they fill all of the acceptance criteria of the ticket.
• If there were infrastructure, operational, or build changes, I have made sure there is sufficient evidence that the changes will work.
• If there were changes that are outside of the regular release processes e.g. account infrastructure to setup, manual setup for external API integrations, secrets to set, then I have checked that the developer has flagged this to the Tech Lead as release steps.
• I have checked that no Personal Identifiable Data (PID) is logged as part of the changes.

[github-actions]

This branch is working on a ticket in the NHS England VED JIRA Project. Here's a handy link to the ticket:

VED-981

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[dlzhry2nhs]

Unless strong objections - and happy to do it in this PR if required - I would propose merging this PR in, subject to approval, as-is so that Lambda function code can be worked on in parallel.

Someone can then pick up the remaining bits of platform changes, but it allows us to at least set up the foundations on the staging branch if we merge asap.

Namely, I think the remaining changes would include:

• KMS encryption for SQS since the data will include PID
• Add DLQ and redrive settings for the outbound mns events queue
• Optional - turn the relevant components into a single mns_publisher module.
• Optional - (might wanna agree testing approach first) add a switch so this feature is only toggled on in environments we want it. May also need to create a test queue for testing that published events are actually broadcast and received by subscribers.

[edhall-nhs]

Nice solution. Good to see it working as well 🎉
Agree that those TODOs can be worked on in parallel with the lambda implementation