arkouda_server refactor with external integration

[hokiegeek2]

This PR basically extends the arkouda_server_refactor PR that was merged last week, encapsulating logic to register Arkouda with external systems--in this PR, specifically as a Kubernetes service) upon Arkouda startup and deregister Arkouda from Kubernetes upon receipt of the ak.shutdown() client request.

This PR consists of the following:

1. ExternalIntegrationServerDaemon class within the ServerDeamon module
2. ExternalIntegration module that encapsulates generalized registerWithExternalSystem and deregisterFromExternalSystem functions that are invoked from the ExternalIntegrationServerDaemon.run() function along with functions that specifically register/deregister Arkouda with/from Kubernetes
3. adds ExternalIntegrationServerDaemon to the getServerDaemon factory function that returns an ArkoudaServerDaemon implementation per a CLI arg
4. EXTERNAL_INTEGRATION.md file that details Arkouda external integration

[Ethan-DeBandi99]

This looks good. For clarity, it would probably be worthwhile documenting why this PR is separate from the standard refactor. The reasoning was clear after we spoke, but it would be good to document.

Posting as comment since this is still a draft

[hokiegeek2]

@mhmerrill @reuster986 @pierce314159 @Ethan-DeBandi99 @joshmarshall1 this is now ready for review. I merged in the final arkouda_server-ServerDaemon refactor, consolidated all register/deregister logic in the ExternalIntegration module and added a EXTERNAL_INTEGRATION.md file linked to the main README.md detailing how things work.

[Ethan-DeBandi99]

I think this looks good to go.