Add [GithubDirectoryFileCount] badge (#5705)

* Added GithubDirectoryFileCount badge

* Additional information on a schema

* Update services/github/github-directory-file-count.service.js

Co-authored-by: Caleb Cartwright <calebcartwright@users.noreply.github.com>

* Update services/github/github-directory-file-count.service.js

Co-authored-by: Caleb Cartwright <calebcartwright@users.noreply.github.com>

* Update services/github/github-directory-file-count.service.js

Co-authored-by: Caleb Cartwright <calebcartwright@users.noreply.github.com>

* More examples

* Moved isArray check to transform method

* Using isMetric for validation

* Added documentaion on type and extension parameters

* Moved a couple of service tests to unit tests

* extension is applicable for type file only

* Note on GitHub API limit

* Using metric helper for a count formatting

Co-authored-by: Caleb Cartwright <calebcartwright@users.noreply.github.com>
Co-authored-by: repo-ranger[bot] <39074581+repo-ranger[bot]@users.noreply.github.com>

services/github/github-directory-file-count.tester.js

@@ -0,0 +1,30 @@
+'use strict'
+
+const { isMetric } = require('../test-validators')
+const t = (module.exports = require('../tester').createServiceTester())
+
+t.create('directory file count').get('/badges/shields.json').expectBadge({
+  label: 'files',
+  message: isMetric,
+})
+
+t.create('directory file count (custom path)')
+  .get('/badges/shields/services.json')
+  .expectBadge({
+    label: 'files',
+    message: isMetric,
+  })
+
+t.create('directory file count (directory not found)')
+  .get('/badges/shields/not_existing_directory.json')
+  .expectBadge({
+    label: 'files',
+    message: 'repo or directory not found',
+  })
+
+t.create('directory file count (not a directory)')
+  .get('/badges/shields/package.json.json')
+  .expectBadge({
+    label: 'files',
+    message: 'not a directory',
+  })