feat: initialize Nonce endpoint

[coplat]

Description of change

This PR initializes the nonce endpoint as described in OID4CI's draft 15 specification. . This is vital as a means to prevent replay attacks during credential requests. Nonces are generated when a post request is made to the /oid4vci/nonce endpoint, returning a unique and fresh c_nonce.

This c_nonce must then be included in the proof of a CredentialRequest made to the issuer. If that nonce has already been redeemed or does not exist, the credential request is denied.

If it is valid, the c_nonce is then marked as redeemed and can no longer be reused.

This PR initializes the nonce endpoint which generates the nonce, and validates the nonce when a credential request is made within the API layer. Further, the nonce commands, events, errors and corresponding aggregate are also initialized within this PR.

Links to any relevant issues

• Blocked by fix: validate all Credentials and nonces in Authorization Response openid4vc#115

How the change has been tested

Existing tests have been updated to include nonces. Nonce endpoint has been added to the postman collection for c_nonce generation.

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
• I have successfully tested this change in a docker environment

[codecov-commenter]

Codecov Report

❌ Patch coverage is 77.27273% with 30 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
agent_event_publisher_http/src/lib.rs	41.17%	10 Missing ⚠️
agent_issuance/src/nonce/event.rs	0.00%	6 Missing ⚠️
...tp/src/v0/issuance/credential_issuer/credential.rs	85.29%	5 Missing ⚠️
agent_issuance/src/nonce/aggregate.rs	85.18%	4 Missing ⚠️
agent_event_publisher_nats/src/lib.rs	0.00%	3 Missing ⚠️
agent_issuance/src/state.rs	50.00%	1 Missing ⚠️
agent_store/src/lib.rs	94.11%	1 Missing ⚠️

Files with missing lines	Coverage Δ
agent_api_http/src/lib.rs	0.00% <ø> (ø)
.../src/v0/issuance/credential_issuer/notification.rs	98.92% <100.00%> (ø)
agent_api_http/src/v0/issuance/mod.rs	100.00% <100.00%> (ø)
agent_api_http/src/v0/issuance/nonce/mod.rs	100.00% <100.00%> (ø)
agent_issuance/src/lib.rs	100.00% <ø> (ø)
agent_issuance/src/nonce/views/mod.rs	100.00% <100.00%> (ø)
agent_issuance/src/server_config/aggregate.rs	49.53% <100.00%> (-0.70%)	⬇️
agent_shared/src/config/mod.rs	91.93% <ø> (ø)
agent_issuance/src/state.rs	54.76% <50.00%> (-0.06%)	⬇️
agent_store/src/lib.rs	72.84% <94.11%> (+0.82%)	⬆️
... and 5 more

... and 1 file with indirect coverage changes

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