Fixes #136

In some cases, we want to have the following schema:

• server.address is a general-purpose attribute defined in server conv

  - id: server
    prefix: server
    attributes:
      - id: address
        brief: 'Domain name.'
       ....

• http semconv wants to define it more narrowly. E.g. update a brief or add HTTP-specific note

- ref: server.address
  brief: Server component of Host header.

• Then HTTP version of this attribute can be used in HTTP traces and metrics.

(see fill example in tests)

Today it works only if semconv extends base HTTP one without mentioning the attribute like

  - id: http.client.request.duration.metric
    type: metric
    metric_name: http.client.request.duration
   ...
    extends: http.client.attributes

Then an attribute is populated from parent semconv as is.

However, if child semconv specifies an attribute even further, it fills it in from the original definition, without considering parent hierarchy first.

I.e.

  - id: http.client.spans
    type: span
   ...
    extends: http.client.attributes
    attributes:
      - ref: server.address
        sampling_relevant: true

resolves to

instead of

The workaround we apply in semconvs is to copy all the notes which is error-prone.

The change implemented here walks up the extended hierarchy and fills in inherited properties in the attribute first.