Adds debug and warn logging around AWS credential chain generation,
specifically to help users debugging auto-unseal problems on AWS, by
logging which role is being used in the case of a webidentity token.
Adds a deferred call to flush the log output as well, to ensure logs
are output in the event of an initialization failure.
* feat: replace the way AWS sessions are created and added a new WebIdentity provider to the credentials chain
* feat: use the correct sdk version
* feat: update go.mod
* feat: remove unnecessary new line
* feat: move AWS_ROLE_SESSION_NAME check up
