Add new HTTP endpoint `/_node/_local/_smoosh/status`. (#4766)

Introduce a new HTTP endpoint `/_node/_local/_smoosh/status`
to get status information from the CouchDB auto-compaction daemon.
Previously, this was only possible by starting a `remsh` session
and manually calling the `smoosh:status/1` function.

The internal data structures of `smoosh:status/1` are migrated
into Erlang maps to send them directly as json to the client.

To add more status information to smoosh in the future, the available
information will be stored under the json key `channels`.

Example:

{
  "channels": {
    "ratio_dbs": { ... },
    "slack_dbs": { ... },
    ...
}
7 files changed