Feat: Support for External Terraform Templates

[Despire]

NOTE: The large number of diff (lines added/deleted) are from restructuring the Protobuf files.

First part of https://github.com/berops/claudie/issues/1441

This PR introduces work with external terraform files which can be downloaded from any publicly available git repository.

The syntax for specifing the template repository was added at the provider level.

  gcp:
    - name: gcp-1
      templates:
        repository: "https://github.com/berops/claudie-config"
        tag: v0.1.2
        path: "templates/terraformer/gcp"
       ...

• if no templates are specified it will always default to the latest commit on the Master/Main branch of the respective cloudprovider on the berops repository.

• if templates are specified, but no tag is present it will default to the latest commit of the Master/Main branch of the respective repository.

The template repository need to follow a certain convention to work properly. For example: If we consider an external template repository accessible via a public git repository at:

https://github.com/berops/claudie-config

The repository may either only contain the necessary templates files or they can be stored at a subtree. To handle this a path is required to be passed along the public git repository such as:

templates/terraformer/gcp

This denotes that the necessary templates for Google Cloud Platform can be found in the subtree at:

claudie-config/templates/terraformer/gcp

To only deal with the necessary template files a sparse-checkout is used when downloading the external repository to have a local mirror present which will then be used to generate the terraform files. When using the template files for generation the subtree present at "claudie-config/templates/terraformer/gcp" the directory is traversed and the following rules apply:

• if a subdirectory with name "provider" is present, all files within this directory will be considered as related to Providers for interacting with the API of respective Cloud Providers, SaaS providers etc. When using the templates for generation, the struct templates.Provider will be passed for each file individually.

• if a subdirectory with name "networking" is present all files within this directory will be considered as related spawning a common networking infrastructure for all nodepools from a single provider. The files in this subdirectory will use the providers generated in the previous step. When using the templates the struct templates.Networking will be passed for each file individually.

• if a subdirectory with name "nodepool" is present all files within this directory will be considered as related to spawning the VM instances along with attached disk and related resources for a single node coming from a specific nodepool. When using the templates the struct templates.Nodepools will be passed for each file individually.

• if a subdirectory with name "dns" is present, all files within this directory will be considered as related to DNS. Thus, the templates.DNS struct will be passed for each file when generating the templates. Note: This subdirectory should contain its own file that will generate the Provider needed for interacting with the necessary API of the respective cloud providers (the ones that will be generated from the "provider" subdirectory will not be used in this case).

The complete structure of a subtree for a single provider for external templates located at claudie-config/templates/terraformer/gcp can look as follows:

└── terraformer
    |── gcp
    │	├── dns
    │   	└── dns.tpl
    │	├── networking
    │		└── networking.tpl
    │	├── nodepool
    │		├── node.tpl
    │		└── node_networking.tpl
    │	└── provider
    │		└── provider.tpl
	...

Examples of external templates can be found on: https://github.com/berops/claudie-config