Add arc42 architecture template to docs.

docs/_toc.yml

docs/dev_guide/architecture/01_introduction_and_goals.md

docs/dev_guide/architecture/02_architecture_constraints.md

docs/dev_guide/architecture/03_system_scope_and_context.md

docs/dev_guide/architecture/04_solution_strategy.md

docs/dev_guide/architecture/05_building_block_view.md

docs/dev_guide/architecture/06_runtime_view.md

docs/dev_guide/architecture/07_deployment_view.md

docs/dev_guide/architecture/08_concepts.md

docs/dev_guide/architecture/09_architecture_decisions.md

docs/dev_guide/architecture/10_quality_requirements.md

docs/dev_guide/architecture/11_technical_risks.md

docs/dev_guide/architecture/12_glossary.md

...e/architecture/images/01_2_iso-25010-topics-EN.drawio.png

docs/dev_guide/architecture/images/05_building_blocks-EN.png

...itecture/images/08-Crosscutting-Concepts-Structure-EN.png

docs/dev_guide/architecture/images/arc42-logo.png

docs/tech/backend.md

docs/tech/indexing.md