refactor(plugins/kuma): refactor custom block plugins specific to Kuma

Remove separate `tip.rb` and `warning.rb` plugins, which were just copies of
the same code with only difference in a block name. Now the code is the same
and just registered for different tags.

It also correctly maps different class names between Kong and Kuma docs.

Signed-off-by: Bart Smykla <[email protected]>

app/_plugins/kuma-specific/custom_block.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+module Jekyll
+  class CustomBlock < Liquid::Block
+    def initialize(tag_name, markup, options)
+      super
+      # Classes differs between Kuma and Kong docs, but they have the same
+      # underlying meanings
+      @class_name = {
+        'tip' => 'note',
+        'warning' => 'important',
+        'danger' => 'warning'
+      }.fetch(tag_name, 'note')
+    end
+
+    def render(context)
+      content = Kramdown::Document.new(super).to_html
+      <<~HTML
+        <blockquote class="#{@class_name}">
+          <p>#{content}</p>
+        </blockquote>
+      HTML
+    end
+  end
+end
+
+Liquid::Template.register_tag('tip', Jekyll::CustomBlock)
+Liquid::Template.register_tag('warning', Jekyll::CustomBlock)
+Liquid::Template.register_tag('danger', Jekyll::CustomBlock)