Add maps for statically vendored components

This change adds a new set of maps for builders, provisioners, and
post-processors that store reference to components that were once part
of Packer and are now vendored. This file acts as a single place for
defining this vendored components, which are then merged into the main
components maps to be used in Packer.

Quick test to ensure the exoscale-import post-processor is still loaded
```
// Validate that exoscale-import is in the know post-procoessors list
~>  packer.test build docker_centos_shell_provisioner.pkr.hcl
Error: Unknown post-processor type "badlynamed-import"

  on docker_centos_shell_provisioner.pkr.hcl line 18:
  (source code not available)

known post-processors: [ucloud-import digitalocean-import docker-push
googlecompute-export manifest vsphere-template docker-tag vsphere checksum
docker-import exoscale-import yandex-export compress googlecompute-import
yandex-import vagrant-cloud alicloud-import amazon-import artifice shell-local
docker-save vagrant]

// Validate that exoscale-import get loaded
~>  packer.test build docker_centos_shell_provisioner.pkr.hcl
Error: Failed preparing post-processor-block "exoscale-import" ""

  on docker_centos_shell_provisioner.pkr.hcl line 18:
  (source code not available)

4 error(s) occurred:

* api_key must be set
* api_secret must be set
* image_bucket must be set
* template_zone must be set

==> Wait completed after 2 microseconds

==> Builds finished but no artifacts were created.
```

command/plugin.go

@@ -1,3 +1,7 @@
+//
+// This file is automatically generated by scripts/generate-plugins.go -- Do not edit!
+//
+
 package command
 
 import (

command/vendored_plugins.go

@@ -6,6 +6,7 @@ import (
 	// Previously core-bundled components, split into their own plugins but
 	// still vendored with Packer for now. Importing as library instead of
 	// forcing use of packer init, until packer v1.8.0
+	exoscaleimportpostprocessor "github.com/exoscale/packer-plugin-exoscale/post-processor/exoscale-import"
 	dockerbuilder "github.com/hashicorp/packer-plugin-docker/builder/docker"
 	dockerimportpostprocessor "github.com/hashicorp/packer-plugin-docker/post-processor/docker-import"
 	dockerpushpostprocessor "github.com/hashicorp/packer-plugin-docker/post-processor/docker-push"
@@ -26,14 +27,15 @@ var VendoredProvisioners = map[string]packersdk.Provisioner{}
 // VendoredPostProcessors are post-processor components that were once bundled with the
 // Packer core, but are now being imported from their counterpart plugin repos
 var VendoredPostProcessors = map[string]packersdk.PostProcessor{
-	"docker-import": new(dockerimportpostprocessor.PostProcessor),
-	"docker-push":   new(dockerpushpostprocessor.PostProcessor),
-	"docker-save":   new(dockersavepostprocessor.PostProcessor),
-	"docker-tag":    new(dockertagpostprocessor.PostProcessor),
+	"docker-import":   new(dockerimportpostprocessor.PostProcessor),
+	"docker-push":     new(dockerpushpostprocessor.PostProcessor),
+	"docker-save":     new(dockersavepostprocessor.PostProcessor),
+	"docker-tag":      new(dockertagpostprocessor.PostProcessor),
+	"exoscale-import": new(exoscaleimportpostprocessor.PostProcessor),
 }
 
-// Upon init lets us load up any plugins that were vendored manually into the
-// default set of plugins.
+// Upon init lets load up any plugins that were vendored manually into the default
+// set of plugins.
 func init() {
 	for k, v := range VendoredBuilders {
 		if _, ok := Builders[k]; ok {

main.go

@@ -1,5 +1,6 @@
 // This is the main package for the `packer` application.
 
+//go:generate go run ./scripts/generate-plugins.go
 package main
 
 import (