Add createSubmit to audit trail filter pattern

[bquenin]

Summary

The WebPostAccessLogger filter pattern was missing createSubmit, which meant that credential creation events (and other resource creation via createSubmit endpoints) were not being logged to the audit trail in Splunk.

Problem

When auditing Jenkins activity via Splunk, credential updates and deletions were properly logged, but credential creations were silently ignored:

Action	Before	After
configSubmit	✅ logged	✅ logged
updateSubmit	✅ logged	✅ logged
doDelete	✅ logged	✅ logged
createSubmit	❌ NOT logged	✅ logged

This is a security gap - there was no way to audit who created a credential from the audit trail.

Fix

Added createSubmit to the FILTER_PATTERN regex in WebPostAccessLogger.java.

Testing

• Added comprehensive unit tests for the filter pattern (WebPostAccessLoggerTest.java)
• Changed pattern visibility from private to package-visible to allow tests to reference the actual pattern (avoiding duplication)
• All 9 tests pass

Verification

This issue was discovered and verified on a production Jenkins controller by:

1. Creating a test credential → No audit event logged (only updated credentials.xml by SYSTEM)
2. Updating the credential → Audit event properly logged with user attribution
3. Deleting the credential → Audit event properly logged with user attribution