Dynamically load Azure dependency for backups

The `fog/azurerm` gem is not loaded by default in `Gemfile`. To make
backups work, we need to load this dynamically when needed.

lib/backup/manager.rb

@@ -196,8 +196,10 @@ module Backup
     end
 
     def connect_to_remote_directory(connection_settings)
+      settings = connection_settings.symbolize_keys
+      load_provider(settings)
       # our settings use string keys, but Fog expects symbols
-      connection = ::Fog::Storage.new(connection_settings.symbolize_keys)
+      connection = ::Fog::Storage.new(settings)
 
       # We only attempt to create the directory for local backups. For AWS
       # and other cloud providers, we cannot guarantee the user will have
@@ -209,6 +211,14 @@ module Backup
       end
     end
 
+    def load_provider(settings)
+      provider = settings[:provider]
+
+      return unless provider.present?
+
+      require 'fog/azurerm' if provider == 'AzureRM'
+    end
+
     def remote_directory
       Gitlab.config.backup.upload.remote_directory
     end

spec/lib/backup/manager_spec.rb

@@ -416,5 +416,28 @@ RSpec.describe Backup::Manager do
         subject.upload
       end
     end
+
+    context 'with AzureRM provider' do
+      before do
+        stub_backup_setting(
+          upload: {
+            connection: {
+              provider: 'AzureRM',
+              azure_storage_account_name: 'test-access-id',
+              azure_storage_access_key: 'secret'
+            },
+            remote_directory: 'directory',
+            multipart_chunk_size: nil,
+            encryption: nil,
+            encryption_key: nil,
+            storage_class: nil
+          }
+        )
+      end
+
+      it 'loads the provider' do
+        expect { subject.upload }.not_to raise_error
+      end
+    end
   end
 end