Add common guidance on recording errors on spans and metrics, clarify DB conventions

[lmolkova]

Fixes #1536

• Document HTTP + DB approach for span status + description as generic for spans
• Document error.type as generic error attribute on spans and metrics
• Specify how to classify db.response.status_codes as failures
• Update recommendation to record exceptions as a span events or log records

Important

We can and should implement strategy of reporting exceptions on local root spans in OTel SDK - it should not be an instrumentation concern.

Here's an OTEP on how to record exceptions on logs - it discusses the details of configurable exception recording strategy.
Since public facing log API is in development, we'll keep using span events for the time being.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.

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Files not reviewed (15)

• docs/database/redis.md: Evaluated as low risk
• docs/database/cassandra.md: Evaluated as low risk
• docs/database/cosmosdb.md: Evaluated as low risk
• docs/rpc/rpc-spans.md: Evaluated as low risk
• docs/messaging/messaging-spans.md: Evaluated as low risk
• docs/cli/cli-spans.md: Evaluated as low risk
• docs/http/http-spans.md: Evaluated as low risk
• docs/general/recording-errors.md: Evaluated as low risk
• docs/gen-ai/gen-ai-spans.md: Evaluated as low risk
• docs/faas/faas-spans.md: Evaluated as low risk
• docs/exceptions/README.md: Evaluated as low risk
• docs/database/elasticsearch.md: Evaluated as low risk
• docs/database/database-spans.md: Evaluated as low risk
• docs/database/mongodb.md: Evaluated as low risk
• docs/database/couchdb.md: Evaluated as low risk