Add support for specifying an external credentials process directly

[gdavison]

Description

The provider can currently use an external credentials process from shared config files with a named profile. Support should be added to directly set it on the provider configuration block.

Potential Terraform Configuration

provider "awscc" {
  # ...
  credential_process {
    command = "..."        # Required. Can be the full command or the executable name
    args    = ["...", ...] # Optional. Can contain arguments for the executable
  }
}

Needs investigation to see if environment variables can be passed as well.

The credentials process can be used along with assume_role but cannot be used with directly passed credentials, profile, or assume_role_with_web_identity.

References

• Will depend on Add support for specifying an external credentials process directly aws-sdk-go-base#291