Python PEP 517/518 support

Is your feature request related to a problem? Please describe.
Frogbot incorrectly assumes that projects with a pyproject.toml file are using the poetry package manager.

Describe the solution you'd like to see
Frogbot would ideally support other build backends that can be specified in pyproject.toml files. Projects with a pyproject.toml file that specify a non-poetry build backend, e.g. setuptools.build_meta should be interpreted following the specification for declaring Python project metadata. Support for other build backends like flit could be added as special cases, but most projects appear to be converging to the standard specification linked above. e.g. old flit style vs new flit style.

[build-system]
build-backend = 'setuptools.build_meta'
requires = ['setuptools']

Additional context
PEP 517 and PEP 518 outline a "build-system independent format" for projects. Common python packaging tools like setuptools have added support for this feature.

Start by tracing how Frogbot interprets pyproject.toml projects and where it assumes Poetry, then read PEP 517/518 and the Python project metadata specification linked in the issue. Done means projects using a non-Poetry backend such as setuptools.build_meta are interpreted from the standard metadata instead of being treated as Poetry projects.