DRIVERS-3617 Specify error.type on OpenTelemetry command spans

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Please complete the following before merging:

• Is the relevant DRIVERS ticket in the PR title?
• Update changelog.
• Test changes in at least one language driver. mongodb/mongo-python-driver#3000 (PYTHON-6045)
• Test these changes against all server versions and topologies (including standalone, replica set, and sharded clusters). Evergreen patch #10898 — 0 failed tasks across standalone, replica set, and sharded cluster on server versions 4.2 through 9.0.

Summary

The OpenTelemetry command span spec already defines db.response.status_code but was missing error.type, which the technical design lists alongside it. error.type is a span-level attribute (distinct from exception.type, carried on the exception event), and tracing backends query and alert on span attributes rather than event attributes — without it, drivers have no shared definition for the dimension backends actually group failures by.

Changes

• Add error.type to the Command Span Attributes table as a required-if-an-error-happens string attribute.
• Specify that error.type SHOULD match db.response.status_code for server errors, and otherwise SHOULD be the exception class name; MUST NOT be set on success; SHOULD have low cardinality.
• Document that error.type deliberately duplicates exception.type and why (span- vs event-level querying).
• State that operation spans MUST NOT carry error.type, since an operation can succeed overall (e.g. via retry) even when an underlying command failed.
• Add a unified test format fixture (error_type.yml/.json) with two cases: a server error, where error.type matches db.response.status_code; and a non-server error (connection closed before a response), where db.response.status_code is absent and error.type falls back to the exception class name. Both cases also assert the operation span has no error.type.
• Add a dated changelog entry to open-telemetry.md.

Testing

• make -C source (YAML → JSON generation, confirmed no diff after regeneration)
• pre-commit run --all-files (mdformat, markdown-link-check, codespell, etc.) — clean
• mkdocs build --strict — clean
• Validated the new fixture's generated JSON against schema-1.27.json with ajv-cli — valid