feat: Add Facter fact for PuppetDB version

The code changes add a new Facter fact called `puppetdb_version` that retrieves the version of PuppetDB installed on the system. It uses the `puppetdb --version` command to fetch the version and returns it as a fact value.

lib/facter/puppetdb_version.rb

@@ -0,0 +1,13 @@
+Facter.add(:puppetdb_version) do
+  confine { Facter::Util::Resolution.which('puppetdb') }
+
+  setcode do
+    output = Facter::Core::Execution.execute('puppetdb --version')
+
+    if output.nil?
+      nil
+    else
+      output.split(':').last.strip
+    end
+  end
+end

spec/unit/facter/puppetdb_version_spec.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'facter'
+
+describe 'puppetdb_version' do
+  subject(:fact) { Facter.fact(:puppetdb_version) }
+
+  before(:each) do
+    Facter.clear
+  end
+
+  it 'should return the correct puppetdb version' do
+    allow(Facter::Util::Resolution).to receive(:which).with('puppetdb').and_return('/usr/bin/puppetdb')
+    allow(Facter::Core::Execution).to receive(:execute).with('puppetdb --version').and_return("puppetdb version: 7.18.0\n")
+
+    expect(Facter.fact(:puppetdb_version).value).to eq('7.18.0')
+  end
+
+  it 'should return nil if puppetdb command is not available' do
+    allow(Facter::Util::Resolution).to receive(:which).with('puppetdb').and_return(nil)
+
+    expect(Facter.fact(:puppetdb_version).value).to be_nil
+  end
+
+  it 'should return nil if puppetdb version output is nil' do
+    allow(Facter::Util::Resolution).to receive(:which).with('puppetdb').and_return('/usr/bin/puppetdb')
+    allow(Facter::Core::Execution).to receive(:execute).with('puppetdb --version').and_return(nil)
+
+    expect(Facter.fact(:puppetdb_version).value).to be_nil
+  end
+end