Add geni.toml file for projects

[emilpriver]

This PRs add the ability to select which database to use via a geni.toml file.

The idea is that you should be able to create a geni.toml file which could look like this:

[production-database]
database_url = "libsql://project"
database_token = "your_database_token_here"

[staging-database]
database_url = "libsql://project-schema"
database_token = "your_database_token_here"

which could allow the user to select the correct database via

geni --project production-database

This pr closes #167