Mark HTTP metric instruments as required or optional

[trask]

What are you trying to achieve?

Clarity on which HTTP metric instruments are required and which are optional.

Additional context.

Initial proposal:

Mark these instruments as required:

• http.server.duration
• http.client.duration

Mark these instruments as optional:

• http.server.active_requests
• http.server.request.size
• http.server.response.size
• http.client.request.size
• http.client.response.size

[trask]

oops, closing, duplicate of #2972