Add documentation for AWS SSM Parameter Store secrets adapter

[davafons]

Documentation for basecamp/kamal#1791

[Copilot]

Pull request overview

Adds documentation for an upcoming aws_ssm_parameter_store secrets adapter to the kamal secrets command docs, including usage examples and a comparison table against other secret backends.

Changes:

• Document AWS SSM Parameter Store as a new secrets source, with fetch/extract examples.
• Add a comparison table covering 1Password vs AWS Secrets Manager vs AWS SSM Parameter Store.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

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[Copilot]

The extract example uses MyItem/REGISTRY_PASSWORD, but the rest of the SSM section uses /myapp/myapp paths and never introduces what MyItem represents for Parameter Store. Align the extract examples with the same naming convention used in the fetch examples to avoid confusion.

Suggested change

	kamal secrets extract MyItem/REGISTRY_PASSWORD <SECRETS-FETCH-OUTPUT>
	kamal secrets extract myapp/REGISTRY_PASSWORD <SECRETS-FETCH-OUTPUT>

[Copilot]

This section labels --from /myapp as fetching "from an item", but the other examples imply --from is a path/prefix in Parameter Store. Consider renaming this heading/text to "from a path/prefix" (or similar) so readers don’t confuse it with an item-based vault model.

Suggested change

	# Fetch passwords from an item
	# Fetch passwords from a path/prefix