fix: DTOSS-8939 Document LetsEncrypt Certificates module and simplify outputs

[patrickmoore-nc]

Description

Add a markdown documentation page, and simplify outputs from LetsEncrypt Certificates module.

• Deployed to Hub Dev:
  https://dev.azure.com/nhse-dtos/dtos-hub/_build/results?buildId=18100&view=results
• Deployed to Hub Prod:
  https://dev.azure.com/nhse-dtos/dtos-hub/_build/results?buildId=18101&view=results

Linked to:

• fix: Simplify letsencrypt-certificates output dtos-hub#85

Context

We don't really need the full details of the pfx blob as its own object (id, location, name, naming_key, subject, versionless_id). This is because when we are consuming this pfx, we need to access the Key Vault Secret resource's value property, and to do that we need to bind it using a data query. For that we only need to know the secret name, and which Key Vault contains it. Consequently we might as well just add pfx_blob_key_vault_secret_name as another property to the existing main key_vault_certificates output object. None of the other pfx_blob properties were needed.

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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