Guide: Show command options for manage providers (#971)

Adding the `--help` output for each provider to the guide for each
managed provider.

This just ensures we always have up-to-date command docs for each
provider.

docs/preprocessor.sh

@@ -22,6 +22,8 @@ cargo run -q --manifest-path ../Cargo.toml -- -q generate-config-schema -o ../ta
 cargo run -q --manifest-path ../Cargo.toml &> ../target/quilkin.commands || true
 cargo run -q --manifest-path ../Cargo.toml -- proxy --help &> ../target/quilkin.proxy.commands || true
 cargo run -q --manifest-path ../Cargo.toml -- manage --help &> ../target/quilkin.manage.commands || true
+cargo run -q --manifest-path ../Cargo.toml -- manage agones --help &> ../target/quilkin.manage.agones.commands || true
+cargo run -q --manifest-path ../Cargo.toml -- manage file --help &> ../target/quilkin.manage.file.commands || true
 cargo run -q --manifest-path ../Cargo.toml -- relay --help &> ../target/quilkin.relay.commands || true
 cargo run -q --manifest-path ../Cargo.toml -- agent --help &> ../target/quilkin.agent.commands || true
 

docs/src/services/xds/providers/agones.md

@@ -7,6 +7,12 @@ This provider watches for changes in Agones
 [`GameServer` resources](https://agones.dev/site/docs/getting-started/create-gameserver/) in a cluster, and
 utilises that information to provide [Endpoint][Endpoints] information to connected Quilkin proxies.
 
+To view all the options for the agones provider subcommand, run:
+```shell
+$ quilkin manage agones --help
+{{#include ../../../../../target/quilkin.manage.agones.commands}}
+```
+
 > Currently, the Agones provider can only discover resources within the cluster it is running in.
 
 ## Endpoint Configuration

docs/src/services/xds/providers/filesystem.md

@@ -2,7 +2,13 @@
 
 The filesystem provider watches a configuration file on disk and sends updates to proxies whenever that file changes.
 
-It can be started with using subcommand `manage file` as the following:
+To view all the options for the file provider subcommand, run:
+```shell
+$ quilkin manage agones --help
+{{#include ../../../../../target/quilkin.manage.file.commands}}
+```
+
+For example:
 ```sh
 quilkin manage file quilkin.yaml
 ```