Add support for fortran-linter

**Name:** Fortran-Linter
**URL:** https://pypi.org/project/fortran_linter/

Fortran syntax checker
Hi,
There is no fortran syntax and style checker in ale, only a wrap around gcc.
I hope, this linter will be of good use.

Please consider adding this.

Start by reviewing the fortran_linter package at the linked PyPI URL and comparing how ALE currently integrates syntax checkers. Identify the relevant integration point and tests, then confirm that Fortran files are checked for syntax and style through the new linter.

Written by the indexing model from the issue text.