Add Provider marker interface and GetCredentialsWithOptions

[waynz0r]

This pull request introduces new provider interfaces and extends the credentials provider functionality in both the rfc7523 and rfc8693 packages. The main goals are to improve type safety and enable option-based configuration for credential retrieval.

Provider interface additions

• Added a new Provider interface with a marker method isRFC7523Provider() to the rfc7523 package, and implemented this method in the credentialsProvider type.
• Added a new Provider interface with a marker method isRFC8693Provider() to the rfc8693 package, and implemented this method in the credentialsProvider type.

Credentials provider enhancements

• Introduced a new GetCredentialsWithOptions method to credentialsProvider in the rfc8693 package, supporting option-based configuration for credential retrieval and improving flexibility in how credentials are requested.