Merge branch 'xmlArtifact' into 'master'

XML artifacts are now served by pages

See merge request !16790

16790-render-xml-artifacts.yml

+---
+title: Render xml artifact files in GitLab
+merge_request: 16790
+author:
+type: added

app/models/ci/artifact_blob.rb

@@ -4,7 +4,7 @@ module Ci
   class ArtifactBlob
     include BlobLike
 
-    EXTENSIONS_SERVED_BY_PAGES = %w[.html .htm .txt .json .log].freeze
+    EXTENSIONS_SERVED_BY_PAGES = %w[.html .htm .txt .json .xml .log].freeze
 
     attr_reader :entry