Validate feasibility of supporting new attribute types

[pellared]

What

Investigate whether it is possible and acceptable to extend the OTel PHP API and SDK with new attribute types.

Guidelines for evolving API/SDK: https://github.com/open-telemetry/opentelemetry-specification/blob/main/oteps/4485-extending-attributes-to-support-complex-values.md#how

Prototype in OTel Go demonstrating feasibility of adding new attribute types: open-telemetry/opentelemetry-go#6809

Why

Per open-telemetry/opentelemetry-specification#4602

Follows open-telemetry/opentelemetry-specification#4614

The goal is to make sure that PRs like these are acceptable for OTel PHP:

• all: drop attribute values restrictions opentelemetry-proto#707
• [EndGoal] [DoNotMerge] Extend the set of attribute value types opentelemetry-specification#4636

[brettmc]

Hi @pellared yes, we could support those attribute types. We actually have to do extra work to disallow complex attributes, and a small test shows that some of the complex attributes suggested in the attached PR work and are accepted by the otel collector:

Resource SchemaURL: https://opentelemetry.io/schemas/1.32.0
Resource attributes:
     <snip>
ScopeSpans #0
ScopeSpans SchemaURL: 
InstrumentationScope io.opentelemetry.contrib.php 
InstrumentationScope attributes:
     -> non-homogeneous: Map({"a":1,"b":2,"enabled":true})
     -> kv: Map({"key1":"value1","key2":"value2"})
     -> bytes: Bytes(gv+XCGYWEoe2Qt1IXS30qw==)
Span #0
    <snip>
Attributes:
     -> app.complex: Map({"bytes":"gv+XCGYWEoe2Qt1IXS30qw==","empty":null,"kv":{"key1":"value1","key2":"value2"},"non-homogeneous":{"a":1,"b":2,"enabled":true}})