update some sslproxy host files to use variables. This will allow nginx to start even if the upstream is not ready

dockerfiles/services/sslproxy/hosts/git.xai-corp.net.conf

@@ -1,12 +1,13 @@
 proxy_cache_path /data/nginx/cache/gitea levels=1:2 keys_zone=gitea:10m max_size=10g
                  inactive=60m use_temp_path=off;
 
-upstream gitea_upstream {
-    server dkhost.xai-corp.net:10080;
-}
-
 # git.xai-corp.net
 server {
+    # this is the internal Docker DNS, cache only for 30s
+    resolver 127.0.0.11 valid=30s;
+
+    set $backend http://dkhost.xai-corp.net:10080;
+
     listen  443 ipv6only=off;
     listen [::]:43 ipv6only=on;
     server_name git.xai-corp.net;
@@ -17,6 +18,6 @@ server {
     add_header Strict-Transport-Security "max-age=15768000; includeSubDomains" always;
 
     location / {
-        proxy_pass http://gitea_upstream;
+        proxy_pass $backend;
     }
 }