Revert "Drop Cache-Control: no-transform usage"

This partially reverts commit 282d979

Ref h5bp/server-configs-apache#185

Author: LeoColomb

h5bp/web_performance/no-transform.conf

@@ -0,0 +1,29 @@
+# ----------------------------------------------------------------------
+# | Content transformation                                             |
+# ----------------------------------------------------------------------
+
+# Prevent intermediate caches or proxies (such as those used by mobile
+# network providers) and browsers data-saving features from modifying
+# the website's content using the `cache-control: no-transform` directive.
+#
+# https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
+# https://tools.ietf.org/html/rfc7234#section-5.2.2.4
+#
+# (!) Carefully consider the impact on your visitors before disabling
+#     content transformation. These transformations are performed to
+#     improve the experience for data- and cost-constrained users
+#     (e.g. users on a 2G connection).
+#
+#     You can test the effects of content transformation applied by
+#     Google's Lite Mode by visiting: https://googleweblight.com/i?u=https://www.example.com
+#
+#     https://support.google.com/webmasters/answer/6211428
+#
+# (!) If you are using `ngx_pagespeed`, note that disabling this will
+#     prevent `PageSpeed` from rewriting HTML files, and, if the
+#     `pagespeed DisableRewriteOnNoTransform` directive isn't set to
+#     `off`, also from rewriting other resources.
+#
+#     https://developers.google.com/speed/pagespeed/module/configuration#notransform
+
+add_header Cache-Control "no-transform";