Add Dictionary Configuration Support

[kevdog824]

PREFACE: I searched open issues for a similar issue but did not find one. Feel free to mark as duplicate if this issue already exists.

I am proposing adding dictionary-based or static configuration-based functionality to Tenacity. I am not sure that this is the best way to describe the functionality I am hoping to see so let me elaborate below.

A convenient part of the standard library logging module is the dictconfig function that allows you to setup configuration for logging from a dictionary. This enables a wide range of options for configuring logging. For example:

• Statically defining the logging configuration via pyproject.toml or some other config file
• Allowing a framework or application runner to easily accept a custom logging definition without custom code (see uvicorn's command line switches for an example of this)

I propose adding a functionality similar to dictconfig to tenacity for creating and configuring Retry objects. I think this would add some good benefits and development options for developers using tenacity.