stages: new bootc.install.config stage

New stage for writing a bootc-install-config with all the options
currently supported.  See bootc-install-config(5).

stages/org.osbuild.bootc.install.config

@@ -0,0 +1,29 @@
+#!/usr/bin/python3
+import pathlib
+import sys
+
+try:
+    import toml
+except ModuleNotFoundError:
+    import pytoml as toml
+
+import osbuild.api
+
+
+def main(tree, options):
+    filename = options["filename"]
+    config = options["config"]
+
+    path = pathlib.Path(tree) / "usr/lib/bootc/install" / filename
+    path.parent.mkdir(parents=True, exist_ok=True)
+
+    with open(path, "w", encoding="utf8") as config_file:
+        toml.dump(config, config_file)
+
+    return 0
+
+
+if __name__ == '__main__':
+    args = osbuild.api.arguments()
+    r = main(args["tree"], args["options"])
+    sys.exit(r)

stages/org.osbuild.bootc.install.config.meta.json

@@ -0,0 +1,78 @@
+{
+  "summary": "Write bootc-install-config(5) file",
+  "description": [
+    "The bootc install process supports some basic customization. This",
+    "configuration file is in TOML format, and will be discovered by the",
+    "installation process in via drop-in files in /usr/lib/bootc/install that",
+    "are processed in alphanumerical order.",
+    "The individual files are merged into a single final installation config, so",
+    "it is supported for e.g. a container base image to provide a default root",
+    "filesystem type, that can be overridden in a derived container image."
+  ],
+  "schema": {
+    "additionalProperties": false,
+    "required": [
+      "filename",
+      "config"
+    ],
+    "properties": {
+      "filename": {
+        "type": "string",
+        "description": "name of the configuration file."
+      },
+      "config": {
+        "additionalProperties": false,
+        "type": "object",
+        "minProperties": 1,
+        "properties": {
+          "install": {
+            "type": "object",
+            "additionalProperties": false,
+            "minProperties": 1,
+            "properties": {
+              "filesystem": {
+                "type": "object",
+                "required": [
+                  "root"
+                ],
+                "additionalProperties": false,
+                "properties": {
+                  "root": {
+                    "type": "object",
+                    "required": [
+                      "type"
+                    ],
+                    "additionalProperties": false,
+                    "properties": {
+                      "type": {
+                        "type": "string"
+                      }
+                    }
+                  }
+                }
+              },
+              "kargs": {
+                "type": "array",
+                "description": "Append extra kernel arguments",
+                "items": {
+                  "type": "string"
+                }
+              },
+              "block": {
+                "type": "array",
+                "description": "An array of supported to-disk backends enabled by this base container image; if not specified, this will just be direct.",
+                "items": {
+                  "type": "string",
+                  "enum": [
+                    "direct",
+                    "tmp2-luks"
+                  ]
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}