Fix: headers and footers are not generated dynamically anymore

The minimal-mistakes theme is using the "jekyll-include-cache" plugin since
version 4.14.0 (see mmistakes/minimal-mistakes#1874).

This change breaks some dynamically generated content, i.e. content
generated from _includes/head/custom.html and _includes/footer.html.

This commit adds a plugin that monkey patches the "include_cached" tag of
"jekyll-include-cache" to disable the caching feature and make it work as
Jekyll's "include" tag.

_plugins/disable-include_cached-tag.rb

@@ -0,0 +1,12 @@
+require "jekyll"
+
+# The minimal-mistakes theme is using the "jekyll-include-cache" plugin since
+# version 4.14.0 (see https://github.com/mmistakes/minimal-mistakes/pull/1874).
+#
+# This change breaks some dynamically generated content, i.e. content
+# generated from _includes/head/custom.html and _includes/footer.html.
+#
+# This plugin monkey patches the "include_cached" tag of "jekyll-include-cache"
+# to disable the caching feature and make it work as Jekyll's "include" tag.
+
+Liquid::Template.register_tag("include_cached", Jekyll::Tags::IncludeTag)