Add Maven artifact resource support for SpotBugs filter files

[Copilot]

• Understand issue Feature Request: Support resolving excludeBugFile/excludeFilterFile/includeFilterFile from remote URLs with authentication #1375 (HTTPS URL + filterServerId)
• Review what the previous task implemented (mvn: scheme — interesting but not what was asked)
• Extend ResourceHelper to fetch http/https URLs with optional Basic auth
• Add filterServerId parameter to SpotBugsMojo; inject Settings + SettingsDecrypter to look up credentials
• Fix sanitization test (was using http URL which now triggers real HTTP fetch)
• Add tests for HTTP URL fetching (with and without auth, and failure cases)
• Update docs (usage.apt.vm)
• Run full test suite — 176 pass, 2 skipped, 0 failures
• Parallel validation — pass; addressed: regex docs, null-decrypter log warning

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud