Allow bitbucket webhook to check atlantis server

[Zophar78]

No description provided.

[Zophar78]

Fix #474

[codecov]

Codecov Report

Merging #475 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master     #475   +/-   ##
=======================================
  Coverage   70.58%   70.58%           
=======================================
  Files          63       63           
  Lines        4246     4246           
=======================================
  Hits         2997     2997           
  Misses       1028     1028           
  Partials      221      221

Impacted Files	Coverage Δ
server/events_controller.go	53.87% <0%> (ø)	⬆️

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[codecov]

Codecov Report

Merging #475 into master will decrease coverage by 0.04%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #475      +/-   ##
==========================================
- Coverage   70.58%   70.53%   -0.05%     
==========================================
  Files          63       63              
  Lines        4246     4249       +3     
==========================================
  Hits         2997     2997              
- Misses       1028     1031       +3     
  Partials      221      221

Impacted Files	Coverage Δ
server/events_controller.go	53.19% <0%> (-0.69%)	⬇️

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[lkysow]

I'd like to pull this logic into a special check ahead of the rest of the code. I want to do this because I don't want there to be more conditionals where we're checking the webhook secret. I think that it might be confusing one day and we might refactor in a way that attackers could bypass the webhook secret checking.

	if eventType == bitbucketserver.DiagnosticsPingHeader {
		// Specially handle the diagnostics:ping event because Bitbucket Server
		// doesn't send the signature with this event for some reason.
		e.respond(w, logging.Info, http.StatusOK, "Successfully received %s event %s=%s", eventType, bitbucketServerRequestIDHeader, reqID)
		return
	}

[lkysow]

Add Header to match the Others.

Suggested change

	DiagnosticsPing = "diagnostics:ping"
	DiagnosticsPingHeader = "diagnostics:ping"

[lkysow]

Thanks!