ghidra: Implement a capa explorer plugin as a Ghidra extension

[colton-gabertan]

Summary

Currently, to use capa's Ghidra UI integration, users must first install and configure Ghidrathon as a separate extension for Ghidra. Ghidrathon's latest release candidate now includes an installation script to both simplify and automate this process. By packaging this with the standalone script, capa_explorer.py, it is now possible to create an official capa explorer plugin for Ghidra.

Motivation

The goal is to create a seamless installation process that allows users to get up and running with the Ghidra Feature Extractor as quickly as possible. This extension will also mirror the functionality of the IDA Pro capa explorer plugin.