Allow to import external locals in volshell environment

[Abyss-W4tcher]

Hi,

this PR adds the possibility to import external locals in a volshell environment. It was needed to import Volshell in the current context, when developing and debugging a plugin.

By the way, this is a cool feature that allows to setup an environment and then analyze created objects efficiently (without pasting and declaring functions directly in volshell). To use it, add the following to your plugin (temporarily of course) :

# Imports
from volatility3.cli.volshell import generic 

# Plugin requirements 
            requirements.PluginRequirement(
                name="volshell", plugin=generic.Volshell, version=(0, 0, 0)
            ),

# Wherever needed
self.context.config[self.config_path + "." + "primary"] = kernel.layer_name
generic.Volshell(self.context, self.config_path).run(additional_locals=locals()) # or even {**locals(), **globals()} if needed
# Then, an interactive session will start :)

[ikelos]

Happy to merge this in, but please also consider the snippets facility of volshell which should allow similar (although not identical) results...