Add is_crash tag

Author: TonyCTHsu

lib/datadog/core/crashtracking/tag_builder.rb

@@ -23,6 +23,7 @@ def self.call(settings)
             'version' => settings.version,
             'git.repository_url' => Environment::Git.git_repository_url,
             'git.commit.sha' => Environment::Git.git_commit_sha,
+            'is_crash' => true
           }.compact
 
           # Make sure everything is an utf-8 string, to avoid encoding issues in downstream

spec/datadog/core/crashtracking/tag_builder_spec.rb

@@ -15,6 +15,7 @@
         'runtime-id' => Datadog::Core::Environment::Identity.id,
         'runtime_platform' => RUBY_PLATFORM,
         'runtime_version' => RUBY_VERSION,
+        'is_crash' => 'true',
       )
     end