This commit fixes a problem where the plugin/AWS SDK would not recognise
static AWS credentials set in the machine's environment variables (by
setting AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY)
The default `WithSharedCredentials` value is `true` in awsutil (v2) -
This essentially disables the ability to read credentials from the
environment because we set the `default` AWS profile options, making the
SDK go search for a profile that may not exist and ignoring the
environment in the way, so we need to set it to `false` (see
`awsutil@v2.(*CredentialsConfig).generateAwsConfigOptions`) for extra
details.