Document the spec export task --filename option

Author: zorbash

lib/mix/tasks/openapi.spec.json.ex

@@ -1,4 +1,5 @@
 defmodule Mix.Tasks.Openapi.Spec.Json do
+  @default_filename "openapi.json"
   @moduledoc """
   Serialize the given OpenApi spec module to a JSON file.
 
@@ -21,12 +22,12 @@ defmodule Mix.Tasks.Openapi.Spec.Json do
     (defaults to true)
 
   * `--quiet` - Whether to disable output printing (defaults to false)
+
+  * `--filename` - The output filename (defaults to "#{@default_filename}")
   """
   use Mix.Task
   require Mix.Generator
 
-  @default_filename "openapi.json"
-
   @impl true
   def run(argv) do
     {opts, _, _} = OptionParser.parse(argv, strict: [start_app: :boolean])

lib/mix/tasks/openapi.spec.yaml.ex

@@ -1,4 +1,5 @@
 defmodule Mix.Tasks.Openapi.Spec.Yaml do
+  @default_filename "openapi.yaml"
   @moduledoc """
   Serialize the given OpenApi spec module to a YAML file.
 
@@ -18,11 +19,12 @@ defmodule Mix.Tasks.Openapi.Spec.Yaml do
     (defaults to true)
 
   * `--quiet` - Whether to disable output printing (defaults to false)
+
+  * `--filename` - The output filename (defaults to "#{@default_filename}")
   """
   use Mix.Task
   require Mix.Generator
 
-  @default_filename "openapi.yaml"
   @dialyzer {:nowarn_function, encoder: 0}
 
   @impl Mix.Task