This adds the new `required_plugins` block to be nested under the packer block.
Example:
```hcl
packer {
required_plugins {
aws = {
version = ">= 2.7.0"
source = "azr/aws"
}
azure = ">= 2.7.0"
}
}
```
For example on darwin_amd64 Packer will install those under :
* "${PACKER_HOME_DIR}/plugin/github.com/azr/amazon/packer-plugin-amazon_2.7.0_x5.0_darwin_amd64"
* "${PACKER_HOME_DIR}/plugin/github.com/hashicorp/azure/packer-plugin-azure_2.7.0_x5.0_darwin_amd64_x5"
+ docs
+ tests
* move maps of plugins back in core
* go mod vendor
* more fixes
* fix imports
* Update core_test.go
* fix build
* more fixes
* more fixes
* up vendors after fixing sdk
* Update post_processor_mock.hcl2spec.go
* Leave implementatino of MapOf in the sdk for plugi tests
Other wise use the interface
* go mod tidy
* add MapOfDatasource type too
