CCM-14410: Make the eventpub lambda handle unknown plane values

[gareth-allan]

Description

This PR adds a check to the eventpub module's lambda to identify events which have a plane field that does not match either data or control, and to DLQ these events rather than silently dropping them as it does now.

Context

I spotted that events with an incorrect plane value could potentially be silently dropped when investigating how the eventpub module could be used to send events to the shared event bus. Note that events with a completely missing plane field would fail the validation step, so are already being DLQed.

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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