Report sanitizer: Add 'kind' if missing

Puppetserver seems to remove 'kind' even from older formats than format
6 when forwarding the report, even if the original reports contains the
key.

lib/puppet/report_sanitizer.rb

@@ -357,6 +357,8 @@ def initialize(
     end
 
     def sanitize(raw)
+      # Puppetserver seems to remove 'kind' even from format version 6 reports.
+      raw['kind'] ||= 'apply'
       sanitized = super
       raw['master_used'] ||= nil
       Util.verify_attributes(raw, %w[noop noop_pending corrective_change master_used])