Add mkdocs-adr-plugin to catalog

[maresin]

What kind of change does this PR introduce?

• Add a project
• Update a project
• Remove a project
• Add or update a category
• Change configuration
• Documentation
• Other, please describe:

Description:
Add mkdocs-adr-plugin – a plugin for MkDocs that adds a floating button to create Architecture Decision Records (ADR) directly from the documentation UI. It includes a modal form with template selection, live editing, automatic numbering, and date substitution. The plugin also provides a CLI wrapper mkdocs-adr that starts both the API backend (FastAPI) and mkdocs serve in one terminal.

Checklist:

• I have read the CONTRIBUTING guidelines.
• I have not modified the README.md file. Projects are only supposed to be added or updated within the projects.yaml file since the README.md file is automatically generated.