fix: Add missing fields to buffered-segments and ingest-spans

[jan-auer]

Adds fields that are present and required on buffered-segments, but have not
been included in its schema. The preceding ingest-spans topic already had
these fields included.

Also exposes MeasurementValue as a named type so we can import it in Sentry.

Ref VIEPF-5
Required by getsentry/sentry#92185

[github-actions]

versions in use:

The following repositories use one of the schemas you are editing. It is recommended to roll out schema changes in small PRs, meaning that if those used versions lag behind the latest, it is probably best to update those services before rolling out your change.

latest version: 1.3.5

changes considered breaking

schemas/buffered-segments.v1.schema.json

• Added a new property, but the consumer has been ignoring additional properties so far. This is probably still fine, but please double-check that the producer does not already send this property with a different type in practice than you defined in this schema.

  {"path": ".spans.?", "change": {"PropertyAdd": {"lhs_additional_properties": true, "added": "data"}}}
  

• Added a new property, but the consumer has been ignoring additional properties so far. This is probably still fine, but please double-check that the producer does not already send this property with a different type in practice than you defined in this schema.

  {"path": ".spans.?", "change": {"PropertyAdd": {"lhs_additional_properties": true, "added": "end_timestamp_precise"}}}
  

• Added a new property, but the consumer has been ignoring additional properties so far. This is probably still fine, but please double-check that the producer does not already send this property with a different type in practice than you defined in this schema.

  {"path": ".spans.?", "change": {"PropertyAdd": {"lhs_additional_properties": true, "added": "start_timestamp_precise"}}}
  

• {"path": ".spans.?", "change": {"RequiredAdd": {"property": "end_timestamp_precise"}}}
  

• {"path": ".spans.?", "change": {"RequiredAdd": {"property": "start_timestamp_precise"}}}
  

⚠️ This PR contains breaking changes. Normally you should avoid that and make
your consumer backwards-compatible (meaning that updated consumers can still
accept old messages). There are a few exceptions:

• If consumers already require these invariants in practice, and you're
  just adjusting the JSON schema to reality, ignore this warning.

• If you know what you are doing, this change could potentially be rolled out
  to producers first, but that's not a flow we support.