Implement configuration file

[paulRbr]

The idea behind this is to be able to configure your bump account locally with a bump config command (and most probably a bump login one to initialize the configuration file)

[scharrier]

The idea here would be to define global --token, --doc and/or --hub. I think that if a user has defined this global context we should display it for each command used.

Also, what would happen if a user adds a --token option but a global context --token as already be set? How do we warn them?

[paulRbr]

As discussed this morning Seb and I, the “context” of a user will make more sense when we will be able to offer User access token.