Add plan for annotation of Inputs and Outputs in v1.1

[garethsb]

IS-13 lets controllers update the label, description and tags of IS-04 resources. IS-08 Inputs and Outputs have a human-readable name and description, but these are read-only in v1.0. There is also no standard place for additional information about an Input or Output, so implementations resort to vendor-specific members in /io.

This PR adds a discussion plan, Annotation Plan. It proposes adding PATCH to IS-08 v1.1, with semantics aligned with IS-13, rather than a separate annotation API. It also explains the tradeoffs against the IS-13 approach. The proposal has three parts:

1. Writable name and description for Inputs and Outputs, including a bulk PATCH /io.
2. tags for Inputs and Outputs, with the same semantics as IS-13.
3. Channel labels, which need more study and input from audio manufacturers and users.

Feedback is welcome, in particular on the scope of the first two parts.