feat: Implement mTLS event stream authentication support

[hsong-rh]

Summary

This PR implements comprehensive mTLS (mutual TLS) authentication support for Event Streams, enabling secure client certificate-based authentication with the Gateway service.

https://issues.redhat.com/browse/AAP-46060

Key Features

• New mTLS Credential Type: EventStreamCredentialType.MTLS for secure client authentication
• Certificate Synchronization: Automatic sync with Gateway API during Event Stream lifecycle
• Certificate Validation: PEM format validation with expiration checking and RFC 2253 subject validation
• Lifecycle Management: Automatic certificate create/update/delete operations

Core Components

• SyncCertificates service for Gateway certificate management
• Enhanced EdaCredential model with mTLS-specific validation
• EventStream views with automatic certificate synchronization
• New API exceptions for Gateway and credential error handling

Security Enhancements

• Certificate format validation using cryptography library
• Subject DN validation with proper X.509 attribute checking
• Secure certificate storage and transmission to Gateway
• Comprehensive error handling for authentication failures

Test plan

• Unit tests for certificate validation logic
• Integration tests for EventStream mTLS workflows
• Service-level tests for Gateway synchronization
• Edge case testing for certificate lifecycle management
• All existing tests continue to pass
• Linting and code quality checks pass

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.64986% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.60%. Comparing base (80bc7b3) to head (655e867).

Files with missing lines	Patch %	Lines
src/aap_eda/core/utils/credentials.py	92.50%	9 Missing ⚠️
tests/integration/api/test_eda_credential.py	94.31%	5 Missing ⚠️
src/aap_eda/api/views/event_stream.py	95.65%	1 Missing ⚠️

@@            Coverage Diff             @@
##             main    #1402      +/-   ##
==========================================
+ Coverage   94.36%   94.60%   +0.24%     
==========================================
  Files         339      343       +4     
  Lines       20006    21111    +1105     
==========================================
+ Hits        18878    19973    +1095     
- Misses       1128     1138      +10     

Flag	Coverage Δ
unit-int-tests-3.11	94.55% <98.64%> (+0.25%)	⬆️
unit-int-tests-3.12	94.60% <98.64%> (+0.24%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/aap_eda/api/event_stream_authentication.py	92.30% <100.00%> (+2.76%)	⬆️
src/aap_eda/api/exceptions.py	100.00% <100.00%> (ø)
src/aap_eda/api/views/eda_credential.py	99.26% <100.00%> (+<0.01%)	⬆️
src/aap_eda/core/exceptions.py	100.00% <100.00%> (ø)
...da/core/management/commands/create_initial_data.py	97.95% <100.00%> (+0.01%)	⬆️
src/aap_eda/services/sync_certs.py	100.00% <100.00%> (ø)
src/aap_eda/utils/logging.py	94.28% <ø> (ø)
tests/integration/api/test_event_stream.py	100.00% <100.00%> (ø)
tests/integration/services/test_sync_certs.py	100.00% <100.00%> (ø)
tests/unit/test_certificate_validation.py	100.00% <100.00%> (ø)
... and 4 more

... and 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
1.7% Duplication on New Code

See analysis details on SonarQube Cloud