feat: implement a very flexible runner for "pre" and "post" scripts

This new functionality now makes it possible to execute scripts at the start or end of the build process, while also being super simple to expand to add further script stages in the future.

It also supports effortless reuse of scripts for multiple stages, since the scripts are now executed with the "current stage" as their 1st argument, to allow them to easily determine which stage they're running in.

build.sh

@@ -32,16 +32,20 @@ if [[ ${#repos[@]} -gt 0 ]]; then
     echo "---"
 fi
 
-# Run scripts.
-get_yaml_array buildscripts '.scripts[]'
-if [[ ${#buildscripts[@]} -gt 0 ]]; then
-    echo "-- Running scripts defined in recipe.yml --"
-    for script in "${buildscripts[@]}"; do
-        echo "Running: ${script}"
-        /tmp/scripts/"$script"
-    done
-    echo "---"
-fi
+# Run "pre" scripts.
+run_scripts() {
+    script_mode="$1"
+    get_yaml_array buildscripts ".scripts.${script_mode}[]"
+    if [[ ${#buildscripts[@]} -gt 0 ]]; then
+        echo "-- Running [${script_mode}] scripts defined in recipe.yml --"
+        for script in "${buildscripts[@]}"; do
+            echo "Running [${script_mode}]: ${script}"
+            /tmp/scripts/"$script" "${script_mode}"
+        done
+        echo "---"
+    fi
+}
+run_scripts "pre"
 
 # Remove RPMs.
 get_yaml_array remove_rpms '.rpm.remove[]'
@@ -77,3 +81,6 @@ if [[ ${#flatpaks[@]} -gt 0 ]]; then
     done
     echo "---"
 fi
+
+# Run "post" scripts.
+run_scripts "post"