Address review comments for dnf_appstream module

- Improve state validation error message.
- Move validation to attribute validators.
- Simplify state checking logic.
- Use info logging for repairs.
- Remove redundant try/except blocks.
- Add test and documentation files.

Author: nickanderson

promise-types/dnf_appstream/README.md

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+# DNF AppStream Promise Type
+
+A CFEngine custom promise type for managing DNF AppStream modules on RHEL 8+ and compatible systems.
+
+## Overview
+
+The `dnf_appstream` promise type allows you to manage DNF AppStream modules, which are a key feature of RHEL 8+ and compatible systems. AppStreams provide multiple versions of software components that can be enabled or disabled as needed.
+
+## Features
+
+- Enable, disable, install, and remove DNF AppStream modules
+- Support for specifying streams and profiles
+- Input validation and sanitization for security
+- Proper error handling and logging
+- Module state checking to avoid unnecessary operations
+- Uses DNF Python API for efficient and secure operations
+
+## Installation
+
+To install this promise type, copy the `dnf_appstream.py` file to your CFEngine masterfiles directory and configure the promise agent:
+
+```
+promise agent dnf_appstream
+{
+  interpreter => "/usr/bin/python3";
+  path => "$(sys.inputdir)/dnf_appstream.py";
+}
+```
+
+## Usage
+
+### Enable a Module
+
+```
+bundle agent main
+{
+  dnf_appstream:
+      "nodejs"
+        state => "enabled",
+        stream => "12";
+}
+```
+
+### Disable a Module
+
+```
+bundle agent main
+{
+  dnf_appstream:
+      "nodejs"
+        state => "disabled";
+}
+```
+
+### Install a Module with Profile
+
+```
+bundle agent main
+{
+  dnf_appstream:
+      "python36"
+        state => "installed",
+        stream => "3.6",
+        profile => "minimal";
+}
+```
+
+### Remove a Module
+
+```
+bundle agent main
+{
+  dnf_appstream:
+      "postgresql"
+        state => "removed";
+}
+```
+
+## Attributes
+
+The promise type supports the following attributes:
+
+- `state` (required) - Desired state of the module: `enabled`, `disabled`, `installed`, or `removed` (default: `enabled`)
+- `stream` (optional) - Specific stream of the module to use
+- `profile` (optional) - Specific profile of the module to install
+
+## Module States
+
+- `enabled` - The module is enabled and available for installation
+- `disabled` - The module is disabled and not available for installation
+- `installed` - The module is installed with its default profile (implies enabled)
+- `removed` - The module is removed or not installed
+
+Note: The `installed` state implies `enabled` because in DNF's module system, installing a module automatically enables it first.
+
+## Security Features
+
+- Input validation and sanitization
+- Module name validation (alphanumeric, underscore, dot, and dash only)
+- Stream name validation (alphanumeric, underscore, dot, and dash only)
+- Uses DNF Python API for secure operations instead of subprocess calls
+- Proper error handling and timeout management
+
+## Requirements
+
+- CFEngine 3.18 or later
+- Python 3
+- DNF Python API (python3-dnf package)
+- DNF package manager (RHEL 8+, Fedora, CentOS 8+)
+- AppStream repositories configured
+
+## Examples
+
+### Enable Multiple Modules
+
+```
+bundle agent enable_development_stack
+{
+  dnf_appstream:
+      "nodejs"
+        state => "enabled",
+        stream => "14";
+
+      "python36"
+        state => "enabled",
+        stream => "3.6";
+
+      "postgresql"
+        state => "enabled",
+        stream => "12";
+}
+```
+
+### Configure Web Server Stack
+
+```
+bundle agent configure_web_server
+{
+  dnf_appstream:
+      "nginx"
+        state => "installed",
+        stream => "1.14";
+
+      "php"
+        state => "installed",
+        stream => "7.4",
+        profile => "minimal";
+}
+```
+
+### Complete Example with Package Installation
+
+```
+promise agent dnf_appstream
+{
+    interpreter => "/usr/bin/python3";
+    path => "$(sys.inputdir)/modules/promises/dnf_appstream.py";
+}
+
+body package_method dnf
+{
+    package_module => "dnf";
+    package_policy => "present";
+}
+
+bundle agent setup_web_server
+{
+    # Enable AppStream modules
+    dnf_appstream:
+        "nodejs"
+            state => "enabled",
+            stream => "14";
+
+        "postgresql"
+            state => "installed",
+            stream => "12";
+
+    # Install packages from the enabled modules
+    packages:
+        # These packages will be installed from the enabled AppStream modules
+        "nodejs" package_method => dnf;
+        "postgresql-server" package_method => dnf;
+        
+        # Standard packages
+        "nginx" package_method => dnf;
+}
+```

promise-types/dnf_appstream/cfbs.json

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+{
+  "name": "dnf_appstream",
+  "type": "promise-type",
+  "description": "A custom promise type to manage DNF AppStream modules",
+  "tags": ["dnf", "appstream", "modules", "package management", "redhat", "fedora", "centos"],
+  "files": [
+    {
+      "path": "promise-types/dnf_appstream/dnf_appstream.py",
+      "type": "source",
+      "permissions": "644"
+    },
+    {
+      "path": "promise-types/dnf_appstream/README.md",
+      "type": "documentation",
+      "permissions": "644"
+    }
+  ],
+  "dependencies": [],
+  "test_command": "python3 test_dnf_appstream.py",
+  "version": "0.0.1"
+}