Handle provider options as in the spec.

[dw-kihara]

As mentioned in issue #70, there is confusion around the aws_credentials_provider:options() type and usage.
I propose introducing the aws_credentials_provider:provider_specific_options() type and passing it to each provider.

Additionally, I suggest two special options that are treated as "common options" for compatibility with current aws_credentials_file users.
I think there are three choices for handling this:

1. Introduce more "common options" in the future if needed.
2. Prohibit any further "common options," keeping them only for compatibility. (my current code)
3. Remove "common options," breaking compatibility.

I prefer option 3 if breaking compatibility is allowed.
I would appreciate your opinions in the comments. 🙇

[dw-kihara]

I realized that the word provider_options is uesd in the aws_credential application env.
So I renamed the provider_options() type to provider_specific_options() in order to avoid confusion.