Improve credentials expiration handling

[dahlb]

https://github.com/dahlb/hatch_rest_api/blob/1745d9c97e477ae540f7ec3e21eaedde2c49dc8f/src/hatch_rest_api/util_bootstrap.py#L36-L40

Not sure if this is the cause, but if you're interested in eliminating periodical reconnecting to the MQTT endpoint in order to have the credentials unexpired, you can provide a callable delegation, which does it automatically, to the credential provider instead of feeding static credentials.

https://awslabs.github.io/aws-crt-python/api/auth.html#awscrt.auth.AwsCredentialsProvider.new_delegate

[dahlb]

looks like this would just change the expiration tracking from the iot connection to the aws token so no changing for now