feat(tracing): add flag to ignore prepare spans in Doctrine (#17219)

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## DESCRIBE YOUR PR
Documentation for the `ignore_prepare_spans` flag, which defaults to
`false` to keep current behaviour intact.
Enabling this will make the SDK produce only one span instead of two per
query (only execute vs prepare + execute)

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## EXTRA RESOURCES

- [Sentry Docs contributor guide](https://docs.sentry.io/contributing/)

Author: Litarnus

docs/platforms/php/guides/symfony/configuration/symfony-options.mdx

@@ -78,6 +78,7 @@ sentry:
         enabled: true
         dbal:
             enabled: true
+            ignore_prepare_spans: false
             connections:
                 - default
         twig:

docs/platforms/php/guides/symfony/tracing/instrumentation/automatic-instrumentation.mdx

@@ -39,6 +39,15 @@ sentry:
       enabled: false
 ```
 
+By default, Doctrine ORM prepares each SQL query before executing it. This leads to traces that contain both `db.sql.prepare` and `db.sql.execute` spans for the same query. Set `ignore_prepare_spans` to `true` to suppress the prepare spans and keep your traces more compact.
+
+```yaml {filename:config/packages/sentry.yaml}
+sentry:
+  tracing:
+    dbal: # DB queries
+      ignore_prepare_spans: true
+```
+
 ## Twig
 
 This integration adds distributed tracing for Twig template rendering using Sentry.