[WIP] Add VSCP as submodule and implement build scripts

[Copilot]

• Add external/vscp as a git submodule (pointing to https://github.com/grodansparadis/vscp)
• Add other required submodules: external/spdlog, external/nlohmann, external/mustache, external/maddy, external/tiny-aes, external/mongoose
• Copy daemon source files from src/vscp/daemon of the vscp project to src/ in this project
• Add CMakeLists.txt for the vscp-daemon build
• Add cmake modules directory with FindMosquitto.cmake, FindEXPAT.cmake, etc.
• Add vcpkg.json for Windows dependency management
• Add GitHub Actions workflow for Linux build
• Add GitHub Actions workflow for macOS build
• Add GitHub Actions workflow for Windows build
• Add install scripts for Linux (install.sh), Windows (install.ps1), and macOS (install-macos.sh)
• Update .gitignore with build artifacts

Original prompt

1. First make the vscp project https://github.com/grodansparadis/vscp a submodule to this project.
2. The move code from src/vscp/daemon in that project to src in this project.
3. Add other missing submodules
4. Add cmake script for the code.
5. Add workflow builds for Linux, Windows and Macintosh
6. Add install script for Linux, Windows and Macintosh.

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