refactor(styles): use JetBrains Mono variable

- Remove Google fonts' "JetBrains Mono" as it didn't support variable
  and add the variable ttf for it

Signed-off-by: Akshit Garg <garg.akshit@gmail.com>

lib/ketbin_web/templates/layout/app.html.eex

@@ -6,9 +6,6 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
     <title>Katbin</title>
     <link rel="stylesheet" href="<%= Routes.static_path(@conn, "/assets/app.css") %>"/>
-    <link rel="preconnect" href="https://fonts.googleapis.com">
-    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
-    <link href="https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;500;600;700;800&display=swap" rel="stylesheet">
     <script defer type="text/javascript" src="<%= Routes.static_path(@conn, "/assets/app.js") %>"></script>
   </head>
   <body class="flex flex-col ">