[exporter/prometheus] add with_resource_as_constant_labels

This add support for the following from the spec:

> A Prometheus Exporter MAY offer configuration to add
> resource attributes as metric attributes. By default,
> it MUST NOT add any resource attributes as metric
> attributes. The configuration SHOULD allow the user
> to select which resource attributes to copy (e.g.
> include / exclude or regular expression based). Copied
> Resource attributes MUST NOT be excluded from target_info.

Signed-off-by: Alex Boten <aboten@lightstep.com>

examples/kitchen-sink.yaml

@@ -125,6 +125,8 @@ meter_provider:
             without_units: false
             without_type_suffix: false
             without_scope_info: false
+            # Configure Prometheus Exporter to add resource attributes as metrics attributes.
+            with_resource_as_constant_labels: "service\\.[.]*"
     # Configure a periodic metric reader.
     - periodic:
         # Configure delay interval (in milliseconds) between start of two consecutive exports.

schema/meter_provider.json

@@ -93,6 +93,9 @@
                 },
                 "without_scope_info": {
                     "type": "boolean"
+                },
+                "with_resource_as_constant_labels": {
+                    "type": "string"
                 }
             }
         },