Add Debian package installation test pipeline with InfluxDB integration

[Copilot]

Adds automated testing of Debian package installation and InfluxDB connectivity on every PR.

Pipeline Implementation

• New test stage in azure-pipelines-ci.yml runs after build stage
• Docker Compose environment with InfluxDB 1.8 and Debian Bookworm containers
• Test template at .azure-pipelines/templates/log4tc/test-deb-installation.yaml

Test Coverage

• Installs Mbc.Log4Tc.Service from GitHub Pages apt repository
• Configures InfluxDB output using production configuration format
• Validates service startup and connection via internal logs at /var/log/log4tc/service.log
• Checks InfluxDB accessibility and database creation
• Publishes service logs as build artifacts

Test Environment

services:
  influxdb:
    image: influxdb:1.8-alpine
    environment:
      INFLUXDB_DB: log4tc
  
  debian-test:
    image: debian:bookworm
    # Installs package, configures InfluxDB output, validates logs

The multi-container setup is extensible for future TwinCAT Docker integration for end-to-end testing.

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