feat: Support ZTIS with XSUAA

[MatKuhr]

Context

This PR improves the credential type detection to deal with a lowercase variant of x509_attested, which will be used by XSUAA.

• E2E tested

Definition of Done

• Functionality scope stated & covered
• Tests cover the scope above
• Error handling created / updated & covered by the tests above
• Documentation updated
• Release notes updated

[MatKuhr]

see the impact of this refactoring. I figured since the feature is very new, SAP internal only and probably not used a lot yet we can accept this

[MatKuhr]

In preparation of removing SecurityLibWorkarounds via #454 (see https://github.com/SAP/cloud-sdk-java-backlog/issues/428 )

Alternatively, one could apply this change standalone in this PR.

[newtork]

I wonder what happens at runtime, or how "hard" this requirement is (or needs to be).

(Update to to xsuaa 3.4.0+ was in sdk 5.8.0 1month ago.)

[MatKuhr]

We would log a warning that we don't recongise X509_ATTESTED, then try to apply BINDING_SECRET but fail with an IllegalSomethingException, because the binding doesn't contain a secret.

[newtork]

I meant: in these lines we are referencing the enum values at runtime directly.

Rendering 3.4.0 the new lower bound for (transitive) security library dependency version. As I said, this may be fine. But we need to be aware of such implications.

Thinking about this, we may be required to define a default case handling in the switch statement, otherwise this code may break for future additions to the enum type.

[MatKuhr]

Good point!

I tried out what happens in a demo application. Turns out: This seems to be fine. I compiled the SDK with version 3.5.0 and then used it in the app with 3.3.5. Nothing bad happens 😄

CredentialType type = SecurityLibWorkarounds.getCredentialType("X509_GENERATED");
System.out.println(type); // x509
System.out.println(List.of(CredentialType.values())); // [x509, instance-secret, binding-secret]

Where I changed SecurityLibWorkarounds.getCredentialType to also include the switch statement, just to quickly run this test.

[newtork]

Please address / take note of my comment here
#453 (comment)

Looks good to me.