feat(stages): Add the ability to set the platform for a stage

integration-tests/test-repo/recipes/stages.yml

@@ -11,6 +11,7 @@ stages:
       - from-file: stages.yml
   - name: fedora-test
     from: fedora
+    platform: linux/amd64
     modules:
       - from-file: stages.yml
   - name: alpine-test

recipe/src/stage.rs

@@ -1,6 +1,6 @@
 use std::path::PathBuf;
 
-use blue_build_utils::syntax_highlighting::highlight_ser;
+use blue_build_utils::{platform::Platform, syntax_highlighting::highlight_ser};
 use bon::Builder;
 use colored::Colorize;
 use miette::{Result, bail};
@@ -23,6 +23,12 @@ pub struct StageRequiredFields {
     /// This is set directly in a `FROM` instruction.
     pub from: String,
 
+    /// Run a stage on a specific platform.
+    ///
+    /// This sets the `--platform` arg on the
+    /// `FROM` instruction.
+    pub platform: Option<Platform>,
+
     /// The shell to use in the stage.
     #[builder(into)]
     #[serde(skip_serializing_if = "Option::is_none")]

template/templates/stages.j2

@@ -54,7 +54,11 @@ COPY cosign.pub /keys/{{ recipe.name|replace('/', "_") }}.pub
   {%- for stage in stages_ext.stages %}
     {%- if let Some(stage) = stage.required_fields %}
 # {{ stage.name|capitalize }} stage
-FROM {{ stage.from }} AS {{ stage.name }}
+FROM \
+      {%- if let Some(platform) = stage.platform %}
+  --platform="{{ platform }}" \
+      {%- endif %}
+  {{ stage.from }} AS {{ stage.name }}
 
 ARG TARGETARCH
       {%- if self::should_color() %}