source-marketo: limit which streams are enabled after discovery

We've observed issues with the the conditional discovery logic for all
the `activity_foobar` bindings. It's not reliable, so sometimes these
bindings are discovered and sometimes they aren't. If these bindings
disappear when they were disabled then are re-discovered later
as enabled, that could blow up certain API limits. To avoid that, I'm
choosing to only enable the bindings that are consistently discovered,
and the remaining conditionally discovered bindings are disabled.

Author: Alex-Bair

airbyte-integrations/connectors/source-marketo/selected_streams.json

@@ -0,0 +1,7 @@
+[
+    "activity_types",
+    "campaigns",
+    "lists",
+    "leads",
+    "programs"
+]