Allow to create credentials without sending them to AWS services

### What feature do you want to see added?

When adding a credential to AWS, the credentials are sent to an AWS endpoint to verify them. Unfortunately there are some plugins that use these credential types (for example the Caching Plugin) to store AWS style credentials that are not used for AWS. It would be useful to disable the credential checking if it is not needed.

### Upstream changes

_No response_

### Are you interested in contributing this feature?

_No response_

Start by tracing the credential-creation path and the AWS endpoint verification described in the issue, including how credential types used by the Caching Plugin are handled. Done means AWS-style credentials can be created without verification when AWS use is not needed, while normal verification remains available.

Written by the indexing model from the issue text.