When set to false, no namespace label will be set by the adapter based on the namespace
portion of the url in the request path.
This allows individual consumers to set namespace independent of the source kubernetes resource.
---
Example:
Given an adapter config like this:
```
externalRules:
- seriesQuery: 'nsq_topic_depth'
resources:
namespaced: false
```
An HPA could target a different namespace by setting it in the selector:
```
- type: External
external:
metric:
name: nsq_topic_depth
selector:
labelSelector:
topic: my-topic
namespace: nsq
```
This is useful for scaling on metrics from services that run in a differnt namespace than the source resource.
This introduces support for the resource metrics in the adapter.
The individual queries and window sizes are fully customizable via a new
config section. This uses just the generic machinery from
metrics-server to serve the API.
This commit introduces advanced configuration. The rate-interval and
label-prefix flags are removed, and replaced by a configuration file
that allows you to specify series queries and the rules for transforming
those into metrics queries and API resources.
