Freezes Packer environment configuration

This is required to have reproducible image build environments.
Frozen component versions:

  * packer = 1.10.0
  * ansible plugin = 1.1.1
  * qemu plugin = 1.0.10
  * vagrant plugin = 1.1.1
  * virtualbox plugin = 1.0.5
  * vmware plugin = 1.0.8

README.md

@@ -18,6 +18,8 @@ $ dnf install ansible-core
 ```
 
 Then follow the Packer installation [instructions](https://developer.hashicorp.com/packer/downloads?product_intent=packer).
+Check the [packer-environment.pkr.hcl](packer-environment.pkr.hcl) file
+for the required Packer version.
 
 Alternatively, you can install a Packer binary from a Yandex
 [mirror](https://hashicorp-releases.yandexcloud.net/packer/): just download a
@@ -27,7 +29,7 @@ Verify that Packer works:
 
 ```shell
 $ packer version
-1.9.4
+1.10.0
 ```
 
 In order to install required Packer plugins run the following command in the

packer-environment.pkr.hcl

@@ -0,0 +1,30 @@
+packer {
+  required_version = "= 1.10.0"
+
+  required_plugins {
+    ansible = {
+      version = "= 1.1.1"
+      source = "github.com/hashicorp/ansible"
+    }
+
+    qemu = {
+      version = "= 1.0.10"
+      source  = "github.com/hashicorp/qemu"
+    }
+
+    vagrant = {
+      version = "= 1.1.1"
+      source = "github.com/hashicorp/vagrant"
+    }
+
+    virtualbox = {
+      version = "= 1.0.5"
+      source  = "github.com/hashicorp/virtualbox"
+    }
+
+    vmware = {
+      version = "= 1.0.8"
+      source = "github.com/hashicorp/vmware"
+    }
+  }
+}