Query IMDSv2 on AWS EC2 to get credentials for KMS if no storepass parameter

[vmal-altium]

This is a solution for #147.

• It does not use AWS Java SDK (too heavy bundle).
• If the storepass parameter is not provided, it queries the Instance MetaData Service (IMDS) to get credentials to access AWS KMS.
• I did not reuse the RESTClient because it assumes JSON response body, and IMDS explicitly returns text, though it may also sometimes be JSON in that text response...

Note

If running from within a container hosted on that EC2, the IMDSv2 may not be reachable by default (hop limit set to 1 for the PUT request to obtain the API token). Updating the hop limit to 2 solves the issue, but this is not managed here. Just a clue in case of breaking tests.

[ebourg]

Thank you for the great PR, comments inline.

[ebourg]

PR merged, thank you!