chore: mark this prebuilt provider package as deprecated (#586)

HashiCorp has made the decision to stop publishing new versions of
prebuilt Terraform `template` provider
bindings for [CDK for Terraform](https://cdk.tf). Once this PR is
merged, this repository will be archived and will no longer
be supported in any way by HashiCorp. Previously-published versions of
this prebuilt provider will still continue to be
available on their respective package managers (e.g. npm, PyPi, Maven,
NuGet), but these will not be compatible with
new releases of `cdktf` and are no longer eligible for commercial
support.
 
As a reminder, you can continue to use the `template` provider in your
CDK for Terraform (CDKTF) projects,
even with newer versions of CDKTF, but you will need to generate the
bindings locally. The easiest way to do so is to use
the [`provider add`
command](https://developer.hashicorp.com/terraform/cdktf/cli-reference/commands#provider-add)
with the `--force-local` flag enabled. For more information, check out our
documentation on [generating provider bindings
manually](https://cdk.tf/imports).

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Signed-off-by: team-tf-cdk <github-team-tf-cdk@hashicorp.com>