text: Title: Web Hook Rules check http headers in case sensitive manner
  Body: ## SUMMARY
  
  The case used for the header name in trigger.headers[<headername>] in a web-hook rule is treated in a case sensitive manner. HTTP headers are case insensitive so the case of the name in the headers should not e relevant.
  
  ### STACKSTORM VERSION
  
  3.2.0
  
  ##### OS, environment, install method
  
  Seen on one-line install and HA
  
  ## Steps to reproduce the problem
  
  See https://github.com/StackStorm/st2/issues/4995 for initial case.
  1. Configure webhookrule with trigger.headers['X-GitHub-Event']
  2. Send in header via curl of X-GitHub-Event to webhook
  3. Rule doesn't match
  4. Change rule to be trigger.headers['X-Github-Event'] - rule matches
  
  ## Expected Results
  
  As http headers are case insensitive then it should not matter what case is used in the rule. Therefore no matter what case header is or case of rule then they should match.
  
  ## Actual Results
  
  Only matched when rule defined as X-Github-Event
  
  