Add .ini version of AWS test credentials
Add .ini version of AWS test credentials

The Go and Rust libraries for AWS access expect credentials files
to be in a different format than the Java library does.

Note that this commit includes private key material, but this is only
for testing and is already public at:
  https://github.com/google/tink/blob/29539107b1de/testdata/

Change-Id: Icd93cd5a4f5c9d1843e753e0da991c35e2686421

project-oak/tink-rust,project-oak/tink-rust,project-oak/tink-rust