Add an api/external endpoint that lists the external services we use.

app/classes/ReleaseInsights/Request.php

@@ -65,6 +65,7 @@ public function getController(): string
             '/about/'                     => 'about',
             '/nightly/'                   => 'nightly',
             '/release/'                   => 'release',
+            '/api/external/'               => 'api/external',
             '/api/nightly/'               => 'api/nightly',
             '/api/release/schedule/'      => 'api/release_schedule',
             '/api/esr/releases/'          => 'api/esr_releases',

app/controllers/api/external.php

@@ -0,0 +1,7 @@
+<?php
+
+declare(strict_types=1);
+
+$json = include MODELS . 'api/external.php';
+
+ReleaseInsights\Utils::renderJson($json);

app/models/about.php

@@ -32,6 +32,10 @@
         <td><a href="/api/nightly/?date={$yesterday}">api/nightly/?date={$yesterday}</a></td>
         <td>Provides the list of nightly build IDs for a day and the changeset they were built from (data from buildhub)</td>
     </tr>
+    <tr>
+        <td><a href="/api/external/">api/external/</a></td>
+        <td>Gives the list of external APIs this site depends on to build data.</td>
+    </tr>
     <tr>
         <td><a href="/api/nightly/crashes/?buildid=20190927094817">api/nightly/crashes/?buildid=20190927094817</a></td>
         <td>Gives the crashes for a buildID (data from Socorro)</td>

app/models/api/external.php

@@ -0,0 +1,5 @@
+<?php
+
+declare(strict_types=1);
+
+return ReleaseInsights\URL::cases();

tests/Functional/api.php

@@ -4,6 +4,7 @@
 
 // Those tests mostly check that our public API works
 $paths = [
+    ['external/', 200, 'Verif:skip'],
     ['nightly/?date=20220101&nocache', 200, '{"20220101095322":"521f2f0038436e8f0a83146ea6c32eb419049b57","20220101231829":"1fe0ce6b31654726691145ca9dc5f2f15114316c"}'],
     ['release/schedule/?version=95', 400, '{
     "error": "API only works with future release."