Add external dependencies CI/CD pipelines with SBOM generation

- Create external-dependencies directory structure with per-package pipelines
- Add DEPENDENCIES-INVENTORY.md with comprehensive dependency tracking
- Create ubuntu-26.04-build-container base image with all dependencies
- Add per-package Jenkinsfiles: log4qt, grantlee, googletest, postgresql, qt6-framework, kdreports
- Add SBOM generation script (generate-sbom.sh) for CycloneDX, SLSA v1.0, and license reports
- Integrate SBOM generation into all Jenkins pipelines
- Add external-dependencies/README.md with usage and security documentation
- Exclude proprietary license files (rti_license.dat) from git tracking

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Entire-Checkpoint: 01M6KNFNMSPW4SY4J4SQTTPVBP

.gitignore

@@ -3,6 +3,7 @@ strix_runs/
 build/
 build_*/
 .envrc
+rti_license.dat
 ArcGIS_Maps_SDK_Qt_linux_300.0.0.zip
 rti_connext_dds-7.7.0-lm-x64Linux4gcc8.5.0.run
 build-rti