Automatize JWT key rotation

[silvin-lubecki]

As a docker scan lambda maintainer,
So I can rotate jwt keys easily,
I want an automatized process which does everything for me.

Tasks

Add a manual triggered github action on the repo.
It needs to:

• create a new ES256 key pair
• Generate the PEM format private key
• Generate the jwks.json with the public key
• optional: fetch the current jwks.json file and add the new key
• Change the private key in the lambda parameter /stage/hub_scan_snyk_jwt/private_signing_key
• Push the jwks.json file to the s3 bucket

[silvin-lubecki]

PR https://github.com/docker/hub.scan-snyk-jwt/pull/16