Email Transport: embed graphs by default (#14270)

* Email embed graphs

* Allow attachment for non-html
Add setting to webui
Correct $auth setting

* Cleanups, throw RrdGraphException instead of returning an error image.
Generate the error image later, giving more control.
Reduce code duplication a little

* Style and lint fixes
Change to flags

* Add baseline for lint errors I don't know how to resolve

* oopsie, changed the code after generating the baseline

* Tiny cleanups.  Make set DeviceCache primary, it is free.

* Docs.

* email_html note

* Allow control of graph embed at the email transport level to override the global config.

* Allow control of graph embed at the email transport level to override the global config.

* Add INLINE_BASE64 to make it easier to create inline image tags

LibreNMS/Alert/Transport/Mail.php

@@ -46,7 +46,7 @@ class Mail extends Transport
             $msg = preg_replace("/(?<!\r)\n/", "\r\n", $obj['msg']);
         }
 
-        return \LibreNMS\Util\Mail::send($email, $obj['title'], $msg, $html);
+        return \LibreNMS\Util\Mail::send($email, $obj['title'], $msg, $html, $this->config['attach-graph'] ?? null);
     }
 
     public static function configTemplate()
@@ -59,6 +59,13 @@ class Mail extends Transport
                     'descr' => 'Email address of contact',
                     'type'  => 'text',
                 ],
+                [
+                    'title' => 'Include Graphs',
+                    'name' => 'attach-graph',
+                    'descr' => 'Include graph image data in the email.  Will be embedded if html5, otherwise attached. Template must use @signedGraphTag',
+                    'type' => 'checkbox',
+                    'default' => true,
+                ],
             ],
             'validation' => [
                 'email' => 'required|email',