chore: bump oid4vc and did_manager dependencies

[nanderstabel]

Description of change

In this change, the oid4vc and did_manager dependencies are updated.

• AGENT_CONFIG_DEFAULT_DID_METHOD environment variable is introduced which can be used to set the DID method that will be used as UniCore's identifier. When not set, it will default to did:key

Blocked by:

• feat: add support for using multiple DID methods openid4vc#70
• chore: bump oid4vc-core dependency did-manager#9

Links to any relevant issues

• Add OpenID4VCI events #23

How the change has been tested

Cross DID method testing is done through the updated test_sign_authorization_request_object test function in agent_verification. With the help of #[rstest], the test will test the use of both did:key and did:jwk.
Manual testing through interaction with UniMe (through this PR: impierce/identity-wallet#197)

Definition of Done checklist

Add an x to the boxes that are relevant to your changes.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes