Refactor the get_model_key util function

[AndreasBBS]

Following the discussion in #300 this refactor moves the function get_model_key() from utils.py to BasePlugin as a staticmethod.

This will allow custom plugin implementations to override the way the model key is generated as described by @kemingy here.

The following example describes how to create a custom flask plugin that does not append the module hash to the model name:

class YourFlaskPlugin(FlaskPlugin):
    def get_model_key(model: ModelType) -> str:
        return f"{model.__name__}"

spec = SpecTree(backend=YourFlaskPlugin)

EDIT:

After lots of attempts to refactor through the staticmethod on the Base Plugin and continuously running into cyclical imports I decided to change course in the implementation. I decided to go with the good old Strategy pattern. Here's the new usage guide:

spec = SpecTree(naming_strategy=lambda model: f"{model.__name__}")

[AndreasBBS]

After lots of attempts to refactor through the staticmethod on the Base Plugin and continuously running into cyclical imports I decided to change course in the implementation.
I decided to go with the good old Strategy pattern. Here's the new usage guide:

spec = SpecTree(naming_strategy=lambda model: f"{model.__name__}")

[kemingy]

Thanks for your contribution! 🎉