Disable crashtracking by default

Crashtracking has been identified as causing issues with `ECHILD` and
`waitpid`, and possibly anything involving `SIGCHLD` with obscure
failure modes of hard to anticipate consequences.

Disable by default as a cautionary measure.

Mitigates #3954

lib/datadog/core/configuration/settings.rb

@@ -886,7 +886,7 @@ def initialize(*_)
           # Enables reporting of information when Ruby VM crashes.
           option :enabled do |o|
             o.type :bool
-            o.default true
+            o.default false
             o.env 'DD_CRASHTRACKING_ENABLED'
           end
         end

spec/datadog/core/configuration/settings_spec.rb

@@ -1967,7 +1967,7 @@
         context 'is not defined' do
           let(:environment) { nil }
 
-          it { is_expected.to be true }
+          it { is_expected.to be false }
         end
 
         [true, false].each do |value|
@@ -1982,9 +1982,9 @@
 
     describe '#enabled=' do
       it 'updates the #enabled setting' do
-        expect { settings.crashtracking.enabled = false }
+        expect { settings.crashtracking.enabled = true }
           .to change { settings.crashtracking.enabled }
-          .from(true).to(false)
+          .from(false).to(true)
       end
     end
   end