stages: add the ability to configure pacman repos

Without configured repositories the generated pacman.conf isn't super
useful. Pacman supports two different ways to configure a repository
either with a Server = line or sourced from pacman's mirrorlist.

stages/org.osbuild.pacman.conf

@@ -15,6 +15,37 @@ SCHEMA = """
     "type": "string",
     "description": "pacman architecture",
     "default": "x86_64"
+  },
+  "repositories": {
+    "type": "array",
+    "items": {
+      "type": "object",
+      "oneOf": [
+        { "required": ["name", "server"] },
+        { "required": ["name", "include"] }
+      ],
+      "properties": {
+        "name": {
+          "type": "string"
+        },
+        "siglevels": {
+          "type": "array",
+          "minLength": 1,
+          "maxLength": 2,
+          "items": {
+            "type": "string",
+            "enum": ["Required", "Optional", "Never", "TrustAll", "TrustedOnly"]
+          }
+        },
+        "server": {
+          "type": "string"
+        },
+        "include": {
+          "type": "string",
+          "default": "/etc/pacman.d/mirrorlist"
+        }
+      }
+    }
   }
 }
 """
@@ -22,12 +53,26 @@ SCHEMA = """
 
 def main(tree, options):
     arch = options.get("architecture", "x86_64")
+    repositories = options.get("repositories", [])
     cfg = f"""
 [options]
 Architecture = {arch}
 SigLevel    = Required DatabaseOptional
 LocalFileSigLevel = Optional
 """
+    for repo in repositories:
+        entry = f"[{repo['name']}]\n"
+        siglevels = repo.get('siglevels', [])
+        include = repo.get('include', '/etc/pacman.d/mirrorlist')
+        if siglevels:
+            siglevelstr = ' '.join(siglevels)
+            entry += f"SigLevel = {siglevelstr}\n"
+        if 'server' in repo:
+            entry += f"Server = {repo['server']}\n"
+        if 'include' in repo:
+            entry += f"Include = {include}\n"
+        cfg += entry + "\n"
+
     os.makedirs(os.path.join(tree, "etc"), exist_ok=True)
     cfgpath = os.path.join(tree, "etc", "pacman.conf")
     with open(cfgpath, "w", encoding="utf-8") as cfgfile: