Register plug-in as Packer integration

[nywilken]

👋 fellow Packer maintainer working on migrating your plugin to the Packer integration framework.

This change takes the necessary steps to register this plugin as an official Packer integration.
Integrations can be found on the Packer integration portal at https://developer.hashicorp.com/packer/integrations.

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The pull-request consists of the following changes:

• Adds controlling, metadata file, metadata.hcl for registering the plug-in and it components as integrations.
  Details on the contents, along with a description of the attributes, can be found at https://github.com/hashicorp/integration-template.
• Adds the GitHub action workflows for triggering manual and automatic integration updates.
• Restructures the plug-in documentation to match the expected format of the integration framework.
• Adds a .web-docs directory for serving the fully render documentation as the integration docs.
• Adds the build-docs make target make build-docs for syncing changes to the docs directory to the .web-docs directory.

Changes to the integration docs can be made at plugin release via the notify-integration-release-via-tag workflow or
manually by running the notify-integration-release-via-manual workflow.

Details on how the Integration framework pipeline works can be found at hashicorp/packer#12702

TODOs

• Open pull-request against external plugin.
• Update integration description .web-docs/metadata.hcl.
• Packer team open internal pull-request to enable integration.
• Review plugin integration on Packer integration portal .... Iterate

[kangasta]

Thanks for the PR! We will take a look at this 👀

[kangasta]

Hello! I merged commits from this PR as part of #51 (as this seemed like a good occasion to complete other maintenance tasks as well).

[nywilken]

@kangasta thanks for merging in the changes with #51. Now that these changes have been merged can you please take a minute to trigger a manual intergration release notification job https://github.com/UpCloudLtd/packer-plugin-upcloud/actions/workflows/notify-integration-release-via-manual.yaml

The version should be set to 1.5.2, which is your latest version. Once completed the integration portal will get updated to pull from this repository. The web cache may take a few minutes to refresh

[nywilken]

Closing since these changes have been merged. Thanks again @kangasta