Expand pool.name in semantic conventions (#3050)

according to the discussion here:
#3038
I'm updating the `pool.name attribute`

CHANGELOG.md

@@ -159,6 +159,8 @@ release.
 
 - Rename built-in ExemplarFilters to AlwaysOn, AlwaysOff and TraceBased.
   ([#2919](https://github.com/open-telemetry/opentelemetry-specification/pull/2919))
+- Expand the declaration of `pool.name`.
+  ([#3050](https://github.com/open-telemetry/opentelemetry-specification/pull/3050))
 - Add `MaxScale` config option to Exponential Bucket Histogram Aggregation.
   ([#3017](https://github.com/open-telemetry/opentelemetry-specification/pull/3017))
 - Rename exponential bucket histogram aggregation to base 2 exponential histogram

specification/metrics/semantic_conventions/database-metrics.md

@@ -58,4 +58,4 @@ Below is a table of the attributes that MUST be included on all connection pool
 
 | Name        | Type   | Description                                                                  | Examples       | Requirement Level |
 |-------------|--------|------------------------------------------------------------------------------|----------------|-------------------|
-| `pool.name` | string | The name of the connection pool; unique within the instrumented application. | `myDataSource` | Required          |
+| `pool.name` | string | The name of the connection pool; unique within the instrumented application. In case the connection pool implementation does not provide a name, then the [db.connection_string](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/semantic_conventions/database.md#connection-level-attributes) should be used. | `myDataSource` | Required          |