Reconsider using constraints

[lmolkova]

constraints allows to formalize that at least one of attributes should be present.

We're getting away from this approach in semconv and usually define an attribute that's always available. Otherwise we use requirement level and notes mechanism to clarify when/how attributes should be populated.

As a result, we use constraints in a very few places in the semconv and it would be great to

• check if we need them there. If we do, we should consider improving markdown rendering (now they appear as See below in the Requirement Level and conflict with ReqLevel on the attribute.
• or remove them from the yaml schema and tooling.

[jsuereth]

We had a mini discussion of this in a smaller group. Given the usage of constraints right now, we'd like to take the following actions:

• Remove all constraints from YAML (schema says their is only "any_of").
• Any-of can migrate to Conditiionally-Required with a note on all attributes.

Additionally, we may want to re-evaluate "any_of" as we think the quality of telemetry in an any_of scenario may be poor for end-users.