chore: add SonarQube code analysis configuration

[joshuapregua]

Summary

• Adds sonar-project.properties with the project key, source paths, test inclusions, and exclusions for auto-generated directories
• Adds .github/workflows/sonar.yaml to run SonarQube analysis and the quality gate on all PRs and pushes to master
• Uses static analysis only, so tests are not run a second time
• Runs on Dependabot PRs, allowing the SonarQube check to be configured as a required status check

Test plan

• Verify the sonarqube check appears and passes on this PR
• After merging, add SonarQube Code Analysis and sonarqube as required status checks on master

[sonarqube-wp-engine-prod]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube