The hcl2_upgrade command transforms a JSON template into an HCL2
template for use with Packer.
The command is quite fragile already, but given that this is the last
remaining fragment that causes Packer to depend on the AWS SDK directly,
we can do away with it.
This commit therefore imports the definitions for AWS access config, so
we can extract this information from the JSON template, and include it
in the definition of the output source for AWS, since we manage this one
differently from other sources.
This allows us to not depend on the AWS plugin directly, which in turn
makes Packer not need to link with the AWS plugin when compiling the
executable.
We are still depending on the AWS SDK for now since the SDK exposes a
aws_secretsmanager function that can be used for interpolation (legacy
JSON interpolation to be clear), so this cannot be removed from now, but
we should consider some form of remediation in the future.
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