CdpCredentialsProvider that chains together multiple credentials
providers. When a caller first requests credentials from this provider,
it calls all the providers in the chain, in the original order specified,
until one can provide credentials, and then returns those credentials. If all
of the credential providers in the chain have been called, and none of them
can provide credentials, then this class will throw an exception indicated
that no credentials are available.
Returns CdpCredentials which the caller can use to authenticate a CDP
request. Each implementation of CdpCredentialsProvider can chose its own
strategy for loading credentials. For example, an implementation might
load credentials from an existing key management system, or load new
credentials when credentials are rotated.