Preview in the context of an existing documentation

[paulRbr]

For now the preview command can only be used to preview a api definition file in one go, without any of the available settings of a Bump documentation (color, logo, grouping, name, etc...).

It would thus be nice if we could preview a file with --doc doc-slug --token doc-token paramters. Thus, we could deploy it to an existing documentation, without impacting the “offical” deploy history.

Note: would it be better to enhance the preview command or add a parameter to the deploy command (e.g. deploy --preview)