doc: update docs and fixed typos (#5821)

rootfs/etc/nginx/lua/certificate.lua

@@ -57,14 +57,14 @@ local function get_pem_cert_uid(raw_hostname)
     return uid
   end
 
-  local wildcard_hosatname, _, err = re_sub(hostname, "^[^\\.]+\\.", "*.", "jo")
+  local wildcard_hostname, _, err = re_sub(hostname, "^[^\\.]+\\.", "*.", "jo")
   if err then
     ngx.log(ngx.ERR, "error: ", err)
     return uid
   end
 
-  if wildcard_hosatname then
-    uid = ngx.shared.certificate_servers:get(wildcard_hosatname)
+  if wildcard_hostname then
+    uid = certificate_servers:get(wildcard_hostname)
   end
 
   return uid

rootfs/etc/nginx/lua/plugins/README.md

@@ -14,7 +14,7 @@ By defining functions with the following names, you can run your custom Lua code
 
  - `init_worker`: useful for initializing some data per Nginx worker process
  - `rewrite`: useful for modifying request, changing headers, redirection, dropping request, doing authentication etc
- - `header`: this is called when backend response header is received, it is useful for modifying response headers
+ - `header_filter`: this is called when backend response header is received, it is useful for modifying response headers
  - `log`: this is called when request processing is commpleted and response is delivered to the client
 
 Check this [`hello_world`](https://github.com/kubernetes/ingress-nginx/tree/master/rootfs/etc/nginx/lua/plugins/hello_world) plugin as a simple example or refer to [OpenID Connect integration](https://github.com/ElvinEfendi/ingress-nginx-openidc/tree/master/rootfs/etc/nginx/lua/plugins/openidc) for more advanced usage.