CLI: Agent version migration tool

[fallwith]

When a new major version of the agent is released, we author a migration guide for current users of the previous major version. This guide will note breaking API changes, deprecated or defunct configuration options, new and/or changed gem instrumentation support, etc.

We should offer a CLI tool that assists users through the migration process.

Essentially... "what parts of the written migration guide can we proactively help a customer see are applicable for their environment?"

So...

• Customer's newrelic.yml is using a now-deprecated or defunct option. Alert!
• Customer's newrelic.yml contains hints that they are using an impacted instrumentation. Alert! (granted, this one's tough because ALL instrumentation is on and opt-out by default)
• Scan the customer's app for calls to API methods we may have changed or removed
• etc.

[workato-integration]

https://issues.newrelic.com/browse/NR-159403

[kford-newrelic]

May or may not be something we want to extend nrdiag to include