Add keep-alive option in webpack devServer

When running the UI locally we were running into the issue of
getting logged off after logging in because of this change:
https://gerrit.openbmc-project.xyz/c/openbmc/bmcweb/+/45175

Adding the keep-alive option in the webpack config prevents this.

Signed-off-by: Dixsie Wolmers <dixsie@ibm.com>
Change-Id: Ic82b4aa1a272d8ea900c240fbe5f527ebe2e608d
diff --git a/vue.config.js b/vue.config.js
index cb33616..0268002 100644
--- a/vue.config.js
+++ b/vue.config.js
@@ -41,6 +41,9 @@
     proxy: {
       '/': {
         target: process.env.BASE_URL,
+        headers: {
+          Connection: 'keep-alive',
+        },
         onProxyRes: (proxyRes) => {
           // This header is ignored in the browser so removing
           // it so we don't see warnings in the browser console