Allow OTEL instrumenter to work even with no DSN.

Context: we are writing tests for our Sentry integration itself,
setting up a client like

```py
events = []
c = sentry_sdk.Client(dsn=None, instrumenter='otel', transport=events.append)
```

, and verifying that events contains spans from OpenTelemetry such as

```py
with tracer.start_as_current_span('fn'):
   raise Exception('boo')

assert events = [...]
```

This currently doesn't work because the Sentry OTEL integration
has some hacks poking into the client and hard-exiting if DSN is None.

I conjecture this can be removed - the check-DSN-to-avoid-sentry-otel-loops
logic still works even without the DSN check in on_start().

sentry_sdk/integrations/opentelemetry/span_processor.py

@@ -113,14 +113,6 @@ def on_start(self, otel_span, parent_context=None):
         # type: (OTelSpan, Optional[context_api.Context]) -> None
         client = get_client()
 
-        if not client.dsn:
-            return
-
-        try:
-            _ = Dsn(client.dsn)
-        except Exception:
-            return
-
         if client.options["instrumenter"] != INSTRUMENTER.OTEL:
             return
 

tests/integrations/opentelemetry/test_span_processor.py

@@ -287,7 +287,16 @@ def test_update_span_with_otel_data_db_query():
     )
 
 
-def test_on_start_transaction():
+@pytest.mark.parametrize(
+    ["dsn"],
+    [
+        pytest.param(
+            "https://[email protected]/123456", id="with a DSN"
+        ),
+        pytest.param(None, id="with no DSN"),
+    ],
+)
+def test_on_start_transaction(dsn):
     otel_span = MagicMock()
     otel_span.name = "Sample OTel Span"
     otel_span.start_time = time.time_ns()
@@ -306,7 +315,7 @@ def test_on_start_transaction():
 
     fake_client = MagicMock()
     fake_client.options = {"instrumenter": "otel"}
-    fake_client.dsn = "https://[email protected]/123456"
+    fake_client.dsn = dsn
     sentry_sdk.get_global_scope().set_client(fake_client)
 
     with mock.patch(