Add basic contribution example base for contribution workflows

[eileenmcnaughton]

Overview

Add basic contribution example base for contribution workflows

The examples have very little exposed tokens so not much is visible - but
it is a start....

Before

Attempting to preview any of the contribution templates, with message admin extension enabled, gives an error

After

A preview page loads - there is not much to see as yet other than some contact data.

Technical Details

Note the Contribution tokens, unlike contact, don't take input of
already loaded data - fixing that will allow quite a lot more stuff to show up (at least where we are using tokens). That would be a good next step

Comments

Note there is some caching so testing this & then pulling the patch & re-testing will not work I use

--- a/Civi/Test/ExampleDataLoader.php
+++ b/Civi/Test/ExampleDataLoader.php
@@ -40,7 +40,7 @@ class ExampleDataLoader {
       $cache = \CRM_Utils_Constant::value('CIVICRM_TEST') ? new \CRM_Utils_Cache_NoCache([]) : \Civi::cache('long');
       $cacheKey = \CRM_Utils_String::munge(__CLASS__);
       $this->metas = $cache->get($cacheKey);
-      if ($this->metas === NULL) {
+      if (1 || $this->metas === NULL) {
         $this->metas = $this->findMetas();
         $cache->set($cacheKey, $this->metas);
       }

[civibot]

(Standard links)

• If this is your first pull-request for CiviCRM, please browse CONTRIBUTING.md for information about the development and testing processes.
• If you are reviewing this pull-request, you may wish to consult the test sites and the Review Standards (long template, short template).

[colemanw]

This feels like a low-risk merge because it's just an example file and some setter functions.