Add action and hook for fypp

[jatkinson1000]

We should add a hook to generate the Fortran source for FTorch from fypp.
This will mean that the full source is in the repo and can be used directly and in documentation.

For developers this would mean they edit the fypp file and then push that, with F90 being generated by the hook.

[jatkinson1000]

A hook has been added as part of #60 but pre-commit hooks cannot modify filed that are committed.
Instead it must warn the user and reject the commit until conditions are met.
Pre-commit hooks cannot be forced upon users, so to keep security on the repo side it should be modified into a workflow.