Adding new required attributes is a breaking change

[lmolkova]

Discussion: #3225 (comment)

Adding new required attributes cannot be handled with schema transformation and would require a major schema version update.

However, spec allows it:

opentelemetry-specification/specification/versioning-and-stability.md

Lines 230 to 236 in e2b9fe0

	In addition to the 3 types of changes described above there are certain types
	that are always allowed. Such changes do not need to be described (and are not
	described) by schema files. Here is the list of such changes:
	- Adding new attributes to the existing semantic conventions for resources,
	spans, span events or log records.
	- Adding new attributes to existing metrics that do not create new timeseries.

[lmolkova]

/ cc @trask @jsuereth

[trask]

We discussed a proposal in the WG meeting Friday to remove Required attributes, replacing them with Conditionally Required, where "Conditionally Required without condition" means instrumentation from this specification version onward must provide it.

I'm wondering if this is needed after the clarification in #3289. I think "Required" now means "instrumentation for this specification version must provide it", and the schema stability rules govern how that can (or cannot) change in future specification versions.

[lmolkova]

I'm fine closing this and considering it's addressed with #3289