make toml optional

[edublancas]

What happens?

if there is a pyproject.toml file but the toml package isn't installed. initializing jupysql fails:

[... long traceback]

ModuleNotFoundError: 'toml' is required to use 'load_toml'. Install with: pip install 'toml'

Instead we should display a message saying that a pyproject.toml was found but that the toml dependency isn't installed.so if the user wants to load the settings, they must install the toml package

To Reproduce

create pyproject.toml and start the extension, ensure the toml package is not installed

OS:

macOS

JupySQL Version:

0.10.0dev

Full Name:

Eduardo Blancas

Affiliation:

Ploomber

[bbeat2782]

Acceptance Criteria

1. If pyproject.toml file is found but the toml package isn't installed, a message should show up instead of the ModuleNotFoundError.
2. Add test function

[edublancas]

go ahead!