Upgrade to TOMLC17, use external dependencies as submodules instead of copied source

[SukuWc]

Todo

• Use https://github.com/cktan/tomlc17 instead the obsolete tomlc99
• Import as submodule to the grid-fw repository
• Pin submodule to release tag of the toml repository
• Update CI workflows to make sure submodules are pulled correctly

Next

• Also use the unittesting framework unity as submodule instead of copied source https://github.com/ThrowTheSwitch/Unity
• Also use littlefs as submodule instead of copied source.