Updating publish instruction for eusc aws account

[sumoanema]

PR Details

Instruction update for publishing layer to EUSC prod account

Description

Listed the steps in contribution.md

Related Issue

Checklist

• Updated CHANGELOG.md.
• Ran unit tests locally.

[Copilot]

Pull request overview

Updates contributor documentation to include release instructions for publishing the Lambda layer to the EUSC (European Sovereign Cloud) production AWS account, alongside existing commercial AWS release steps.

Changes:

• Adds a new “Releasing layer for Commercial AWS” subsection heading to clearly separate existing steps.
• Adds a new “Releasing layer for EUSC … AWS” section describing credential/profile setup and the special-partitions publish script.

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