Need a way to install third party plugins that is easier, and survives upgrade

The current procedure for installing third party plugins is unnecessarily complex.  Here's a good writeup of what is needed:

https://github.com/mpoindexter/nexus-repository-apt#most-permanent-install

This has a number of problems.

1. It is very complex
2. Different configuration files are used for OSS vs. Pro. This means a bundle can be lost after installing a license
3. The installation configuration is in the installation directory, not the work directory. This means it will not survive an upgrade

And worse, a misconfigured or missing bundle can cause the server not to start (NEXUS-14671).

There should be an easier way to install 3rd party plugins.  And any configuration needed should be located in the work directory, not the installation directory.