ref(span-v2-sdk): Add sentry.span.source attribute to common attributes list (#15946)

Author: Lms24

develop-docs/sdk/data-model/event-payloads/transaction.mdx

@@ -181,6 +181,12 @@ _Optional_. An object containing standard/custom measurements with keys signifyi
 
 ## Transaction Annotations
 
+<Alert level="info">
+
+Span name source information MUST still be set for Span v2 segment spans, although via a span attribute. See [Span v2 Protocol](/sdk/telemetry/spans/span-protocol/#common-attribute-keys) for more information.
+
+</Alert>
+
 `transaction_info`
 
 _Recommended_. Additional information about the name of the transaction.

develop-docs/sdk/telemetry/spans/span-protocol.mdx

@@ -168,6 +168,7 @@ Empty attributes must be omitted.
 | `sentry.environment` | string | The environment name (e.g., "production", "staging", "development") |
 | `sentry.segment.name` | string | The segment name (e.g., "GET /users") |
 | `sentry.segment.id` | string | The segment span id |
+| `sentry.span.source` | string | The source of the span name. **MUST** be set on segment spans, **MAY** be set on child spans. <br/> See [Sentry Conventions](https://github.com/getsentry/sentry-conventions/attributes/sentry#sentry-span-source) for all supported sources. <br/>See [Transaction Annotations](/sdk/data-model/event-payloads/transaction/#transaction-annotations) and [Clustering](/backend/application-domains/transaction-clustering/#automatic-transaction-clustering) for more information.|
 | `os.name` | string | The operating system name (e.g., "Linux", "Windows", "macOS") |
 | `browser.name` | string | The browser name (e.g., "Chrome", "Firefox", "Safari") |
 | `user.id` | string | The user ID (gated by `sendDefaultPii`) |