Fix link to DB semconv (#4760)

CI link check is failing since the page was moved in
open-telemetry/semantic-conventions#3108.

Using otel.io link instead since we make extra effort to keep them
working when links change.

Author: lmolkova

specification/trace/api.md

@@ -764,7 +764,7 @@ are built and instrumented.
 [Semantic conventions](../overview.md#semantic-conventions) for
 specific technologies should document kind for each span they define.
 
-For instance, [Database Client Semantic Conventions](https://github.com/open-telemetry/semantic-conventions/blob/main/docs/database/database-spans.md)
+For instance, [Database Client Semantic Conventions](https://opentelemetry.io/docs/specs/semconv/database/database-spans/)
 recommend using `CLIENT` span kind to describes database calls.
 If the database client communicates to the server over HTTP, the HTTP
 instrumentation (when enabled) creates nested `CLIENT` spans to track individual