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

external-dependencies/postgresql/Dockerfile

@@ -0,0 +1,26 @@
+# PostgreSQL Installation
+FROM harbor.sl.defence-elec.de/proxydockerhub/library/ubuntu:26.04
+
+LABEL maintainer="Legatus Team"
+LABEL description="PostgreSQL client libraries"
+LABEL version="16"
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+ARG HTTP_PROXY=""
+ARG HTTPS_PROXY=""
+ARG NO_PROXY="localhost,127.0.0.1,.sl.defence-elec.de"
+
+ENV http_proxy=${HTTP_PROXY}
+ENV https_proxy=${HTTPS_PROXY}
+ENV no_proxy=${NO_PROXY}
+
+# Install PostgreSQL client libraries
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    libpq-dev postgresql-client \
+    && rm -rf /var/lib/apt/lists/*
+
+# Verify installation
+RUN psql --version | grep -q "16"
+
+CMD ["/bin/bash"]