Update proxy and docs for Kamal 2.0/kamal-proxy 0.3.0

Update to kamal-proxy 0.3.0 and improve docs making sure they are in
sync with that version.

lib/kamal/configuration/docs/proxy.yml

@@ -1,5 +1,9 @@
 # Proxy
 #
+# Kamal uses [kamal-proxy](https://github.com/basecamp/kamal-proxy) to provide
+# gapless deployments. It runs on ports 80 and 443 and forwards requests to the
+# application container.
+#
 # The proxy is configured in the root configuration under `proxy`. These are
 # options that are set when deploying the application, not when booting the proxy
 #
@@ -13,20 +17,25 @@ proxy:
   # to this host to your app.
   #
   # If no hosts are set, then all requests will be forwarded, except for matching
-  # requests for other apps that do have a host set.
+  # requests for other apps deployed on that server that do have a host set.
   host: foo.example.com
 
   # App port
   #
   # The port the application container is exposed on
+  #
   # Defaults to 80
   app_port: 3000
 
   # SSL
   #
-  # Kamal Proxy can automatically obtain and renew TLS certificates for your applications.
-  # To ensure this set, the ssl flag. This only works if we are deploying to one server and
-  # the host flag is set.
+  # kamal-proxy can provide automatic HTTPS for your application via Let's Encrypt.
+  #
+  # This requires that we are deploying to a one server and the host option is set.
+  # The host value must point to the server we are deploying to and port 443 must be
+  # open for the Let's Encrypt challenge to succeed.
+  #
+  # Defaults to false
   ssl: true
 
   # Deploy timeout
@@ -36,8 +45,8 @@ proxy:
 
   # Response timeout
   #
-  # How long to wait for requests to complete before timing out, defaults to 10 seconds
-  response_timeout: 30s
+  # How long to wait for requests to complete before timing out, defaults to 30 seconds
+  response_timeout: 10s
 
   # Healthcheck
   #
@@ -70,7 +79,7 @@ proxy:
   #
   # Configure request logging for the proxy
   # You can specify request and response headers to log.
-  # By default, Cache-Control and Last-Modified request headers are logged
+  # By default, Cache-Control, Last-Modified and User-Agent request headers are logged
   logging:
     request_headers:
       - Cache-Control
@@ -84,4 +93,7 @@ proxy:
   # Whether to forward the X-Forwarded-For and X-Forwarded-Proto headers (defaults to false)
   #
   # If you are behind a trusted proxy, you can set this to true to forward the headers.
+  #
+  # By default kamal-proxy will not forward the headers the ssl option is set to true, and
+  # will forward them if it is set to false.
   forward_headers: true