[bootloader] Fix up schema

src/modules/bootloader/bootloader.schema.yaml

@@ -4,15 +4,30 @@ $id: https://calamares.io/schemas/bootloader
 additionalProperties: false
 type: object
 properties:
-    efiBootLoader: { type: string, required: true }
+    efiBootLoader: { type: string }
-    kernel:  { type: string, required: true }
+    kernel:  { type: string }
-    img:  { type: string, required: true }
+    img:  { type: string }
-    fallback:  { type: str }
+    fallback:  { type: string }
-    timeout:  { type: str }
+    timeout:  { type: string }  # Inserted verbatim
-    bootloaderEntryName:  { type: str }
+    bootloaderEntryName:  { type: string }
-    kernelLine:  { type: str }
+    kernelLine:  { type: string }
-    fallbackKernelLine:  { type: str }
+    fallbackKernelLine:  { type: string }
-    grubInstall:  { type: string, required: true }
+
-    grubMkconfig:  { type: string, required: true }
+    # Programs
-    grubCfg:  { type: string, required: true }
+    grubInstall:  { type: string }
-    efiBootloaderId:  { type: str }
+    grubMkconfig:  { type: string }
+    grubCfg:  { type: string }
+    grubProbe: { type: string }
+    efiBootMgr: { type: string }
+
+    efiBootloaderId:  { type: string }
+    installEFIFallback: { type: boolean }
+
+required:
+    - efiBootLoader
+    - kernel
+    - img
+    - grubInstall
+    - grubMkconfig
+    - grubCfg
+    - grubProbe