Update CI to vcpkg / Add Unit tests

[MatthiasHertel80]

The CI still uses AWS AMI. Update this to use vcpkg tool installation as used in CMSIS-DSP
https://github.com/ARM-software/CMSIS-DSP/blob/main/.github/workflows/runcpptest.yaml

The Unit Tests could be added to another workflow.

[FabKlein]

I think this is covered now.
The updated CI has moved to vcpkg-based tool installation, and the unit tests are split into dedicated workflows:

• https://github.com/ARM-software/CMSIS-NN/blob/main/vcpkg-configuration.json
• https://github.com/ARM-software/CMSIS-NN/blob/main/.github/workflows/integer-fvp.yml
• https://github.com/ARM-software/CMSIS-NN/blob/main/.github/workflows/float-fvp.yml
• https://github.com/ARM-software/CMSIS-NN/blob/main/.github/workflows/lib-variants.yml

I believe this issue can probably be closed.