Credentials caching docs are not discoverable

### Describe the issue

Customers looking at the [`SdkConfig`](https://docs.rs/aws-config/latest/aws_config/struct.SdkConfig.html#method.credentials_cache) docs, or other root configuration pieces of the aws-config crate, have to click through several layers of types in order to arrive at the [`LazyBuilder`](https://docs.rs/aws-credential-types/0.55.3/aws_credential_types/cache/struct.LazyBuilder.html) docs in order to see what is configurable on credentials caching.

This discovery pathway needs to be improved (and should also be improved on the generated service config).

### Links

See above.

Start with the linked SdkConfig and LazyBuilder documentation, then inspect the aws-config root configuration docs and the generated service config documentation. The work is done when credentials-caching configuration is discoverable from those entry points without requiring several layers of navigation.

Written by the indexing model from the issue text.