Load testimonials by tag instead of by name

- Allow loading testimonials by tag instead of name.
- Remove the code to load testimonials by name.
- Add a `limit` and `offset` to create different lists on the same page
  - e.g. on the team coaching page where I have two testimonial
  sections.

source/_includes/testimonials.html.twig

@@ -1,36 +1,19 @@
-{% set defaultNames = [
-  "Matthieu Scarset",
-  "Mike Karthauser",
-  "Tawny Bartlett",
-  "Joe Howell",
-  "Jon Hallett",
-  "Michael Itkoff",
-  "Mick Felton",
-  "Duncan Davidson",
-  "Adam Cuddihy",
-  "Huw Davies",
-  "Scott Euser",
-  "Brian Hartwell",
-  "Alan Hatch",
-  "Holly Ross",
-  "Josh Mitchell",
-  "Brian Healy",
-  "Chris Jarvis",
-  "Daniel Easterbrook",
-  "Anonymous",
-] %}
+{% set limit = limit ?? 10 %}
+{% set offset = offset ?? 0 %}
 
-{% if not merge %}
-  {% set names = names|default(defaultNames) %}
-{% else %}
-  {% set names = names|merge(defaultNames) %}
+
+{% set testimonials = site.testimonials %}
+{% if tag is not null %}
+  {% set testimonials = testimonials|filter(testimonial => tag in testimonial.tags) %}
 {% endif %}
 
+{% set testimonials = testimonials|slice(offset, limit) %}
+
 <section>
   <h2 class="text-xl font-bold">{{ title|default('Testimonials') }}</h2>
 
   <div class="mt-4 space-y-12">
-    {% for testimonial in site.testimonials|filter(testimonial => names is null or testimonial.name in names) %}
+    {% for testimonial in testimonials %}
       <div>
         <div class="italic prose prose-p:text-black prose-a:font-light prose-a:text-blue-primary prose-p:text-lg prose-blockquote:border-blue-primary dark:marker:text-white prose-li:my-1 prose-li:text-lg prose-figcaption:text-white prose-li:text-black marker:text-black dark:prose-p:text-white dark:prose-invert dark:prose-a:text-blue-400 dark:prose-blockquote:border-blue-400 dark:prose-li:text-white hover:prose-a:no-underline prose-h2:text-xl prose-code:font-normal prose-h2:mb-4 prose-ul:my-3 dark:prose-hr:border-grey-400 prose-code:before:content-[''] prose-code:after:content-['']">
         <blockquote>