Clarify metric SDK views section

[MrAlias]

• Break the metric SDK views section into sub-sections. This provided structure helps define normative requirements hierarchically and clearly (required inputs are separated from their definitions).
  • Split the list of view inputs into their own sections.
  • Split the suggested implementation of View resolution into its own section.
  • Split the Python examples into their own section.
• Clarify the normative requirements and optionality to the views input. Currently the input parameters are (mostly) accompanied by terms like (required) or (optional). These terms have not normative value in the specification and are not clear about who their subject is (i.e. SDK author or SDK user).
  • Clarify the instrument selection criteria are all required to be implemented but optional for a user to provide.
  • Clarify the stream configuration parameters are all required to be implemented but optional for a user to provide.
• Move the view name to be the name parameter of a stream configuration.

[pellared]

@MrAlias Feel free to resolve my comments.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 7 days.

[jmacd]

I see a the concerns about optionality to the user and optionality to the SDK and would be glad to see those improved in a future PR. I think this change is a big improvement either way.