Split v2 /node/logging API into separate GET and PUT APIs

Currently, the /v2/node/logging API (and it's v1 counterpart: /solr/admin/info/logging) use the same API to both set and get log-level information.

In the v2 world at least, this could be split up to depend on the HTTP verb, using POST or PUT for changes to log-levels, and GET for retrieval of log-level information.

Doing so would be more consistent with the HTTP-verb-aware design of the v2 API.  Practically though, it'd also help us get around a limitation of the current annotation framework, where each API can only be governed by a single PermissionNameProvider.Name value.  Splitting the APIs into different verbs lets us govern them with the appropriate permissions in v2-land.