SOLR-18091: Separate out core specific info into CoreInfoHandler

[epugh]

https://issues.apache.org/jira/browse/SOLR-18091

Description

Instead of having SystemInfoHandler accessible at two different URLS, and serving different data, just split them and have proper names.

V1: http://localhost:8983/solr/admin/info/system
V2: http://localhost:8983/api/node/system

and

http://localhost:8983/solr/techproducts/admin/info

There appears to be no V2 for the core level

Solution

Make loading pattern clearer. CoreInfoHandler is in ImplicitPlugins.json, while SystemInfoHandler is part of InfoHandler loaded in CoreContainer.

Tests

manual and unit

I still need to check the solr Admin UI to make sure the new /solr/techproducts/admin/info url makes.

[epugh]

Does this request handler need if (AdminHandlersProxy.maybeProxyToNodes(req, rsp, getCoreContainer(req))) { like SystemInfoHandler has? Is that soemthing every class needs?

[epugh]

@gerlowskija @igiguere you may be interested in this PR with your work on the V2 apis...

[epugh]

I think this could go to 10x as it turns out the Admin UI, which is the primary consumer, was easy to update.

[epugh]

I think that the fact that you got system info at the core level was a bug... not a feature. And that by seperating them and making the urls endpoints clearer, I fixed the bug, and therefore this can be backported to branch_10x.... Thoughts?

[igiguere]

@gerlowskija @igiguere you may be interested in this PR with your work on the V2 apis...

@gerlowskija @igiguere you may be interested in this PR with your work on the V2 apis...

I was working on #4078 instead. Draft... a couple of questions before I make it official.
I agree that system info should not need the core info. (I think I commented about in a unit test somewhere.)
See NodeSystemInfoProvider in #4078 : it gathers the methods to get the info, including core info... so maybe that could be elsewhere when core info is separate from system info

[epugh]

Okay, this looks ready for final review and hopefully a merge!