open-telemetry#5110)

Follows
open-telemetry#5028

Per
open-telemetry#5028 (comment):

>> An attribute set is analogous to a map.
>
> It is not specified anywhere. It a subject for a separate PR as we
would need it for
open-telemetry/opentelemetry-go#8209. I do not
want to open large PRs and I plan to create it once this PR lands.

It will also unblock
open-telemetry/opentelemetry-go#8209 (after
being stable).

### Context

- Clarify that environment variable propagation carriers normalize
requested
  keys, carrier keys, and returned keys.

([open-telemetry#5102](open-telemetry#5102))
- Specify that environment variable propagation carriers only read and
return
  normalized environment variable names.

([open-telemetry#5144](open-telemetry#5144))
- Specify that an empty environment variable propagation name is
non-normalized
  and normalizes to `_`.

([open-telemetry#5163](open-telemetry#5163))

### Profiles

- Remove duplicate information from and extend Profiles documentation
(README.md, pprof.md).

([open-telemetry#4932](open-telemetry#4932))

### Entities

- Add specification for communicating entity information as structured
log events.

([open-telemetry#4836](open-telemetry#4836))

### Common

- Add an in-development [SDK
self-observability](specification/self-observability.md)
  section, referenced from the Tracing, Metrics, and Logs SDK specs.

([open-telemetry#5087](open-telemetry#5087))
- Clarify non-OTLP representation guidance for nested `AnyValue` values
in
  arrays and maps.

([open-telemetry#5053](open-telemetry#5053))
- Add in-development guidance recommending a JSON object as the string
  representation for an attribute in non-OTLP protocols.

([open-telemetry#5028](open-telemetry#5028))
- Add in-development guidance recommending a JSON object as the string
  representation for an attribute collection in non-OTLP protocols.

([open-telemetry#5110](open-telemetry#5110))

### Compatibility

- Deprecate OpenCensus compatibility requirements in the specification.

([open-telemetry#5138](open-telemetry#5138))
- Stabilize sections of Prometheus Metrics Exporter.
  - Clarify resource attributes configuration.

([open-telemetry#5084](open-telemetry#5084))
- Stabilize the conversion of OTLP Summaries into Prometheus Summaries.

([open-telemetry#5107](open-telemetry#5107))
  - Stabilize client libs section.

([open-telemetry#5106](open-telemetry#5106))
- Stabilize Prometheus Metrics Exporter default aggregation
configuration.

([open-telemetry#5113](open-telemetry#5113))
- Stabilize sections of Prometheus and OpenMetrics Compatibility.
- Stabilize OpenTelemetry Histogram to Prometheus Histogram
transformation.

([open-telemetry#5091](open-telemetry#5091))
- Add optional OpenTelemetry Histogram to Prometheus Native Histogram
with Custom Buckets transformation.

([open-telemetry#5091](open-telemetry#5091))

### SDK Configuration

- Add link to declarative config IdGenerator type

([open-telemetry#5133](open-telemetry#5133))

### OTEPs

- Context-scoped Attributes.

([open-telemetry#4931](open-telemetry#4931))

---------

Co-authored-by: Reiley Yang <reyang@microsoft.com>