Add support for specifying the workspace manifest file name

Includes an additional scenario illustrating a custom manifest file name
in the README file.

README.md

@@ -62,4 +62,15 @@ the necessary modules for a West based [Zephyr workspace application][1].
     sdk-version: 0.16.3
 ```
 
+## Specify a custom west workspace manifest file name
+
+```yaml
+- name: Setup Zephyr project
+  uses: zephyrproject-rtos/zephyr-setup@v1
+  with:
+    app-path: app
+    toolchains: arm-zephyr-eabi
+    manifest-file-name: custom_west.yml
+```
+
 [1]: https://docs.zephyrproject.org/latest/develop/application/index.html#zephyr-workspace-app

action.yml

@@ -6,9 +6,15 @@ description: Setup a Zephyr base project using west and downloading the Zephyr S
 
 inputs:
   app-path:
-    description: Application code path, should contain a west.yml file
+    description: |
+      Application code path, should contain a west.yml file if "manifest-file-name" is not specified
     required: true
 
+  manifest-file-name:
+    description: Name of the west workspace manifest file name in "app-path"
+    required: false
+    default: west.yml
+
   sdk-version:
     description: Zephyr SDK version to use or "auto" to detect automatically
     required: false
@@ -54,7 +60,7 @@ runs:
     - name: Initialize
       shell: bash
       run: |
-        west init -l ${{ inputs.app-path }}
+        west init -l ${{ inputs.app-path }} --mf ${{ inputs.manifest-file-name }}
         west update -o=--depth=1 -n
 
     - name: Environment setup