feat(coderd_template): Support also referencing an archive file.

Similar to the `coder templates push` command, the coderd_template resource should be able to optionally reference an archive file to push instead of just a directory.

I have a use-case where I need to be able to include hidden directories as part of the template bundle, and to my understanding the way Coder handles it, it intentionally ignores them.

In my use-case, I'm already filtering out the hidden files that I shouldn't be including via:
```
tar \
--exclude='tmp.auto.tfvars.json' \
--exclude='tf.plan' \
--exclude='terraform.tfstate' \
--exclude='.claude' \
--exclude='.terraform' \
--exclude='._*' \
--exclude='.DS_Store' \
--exclude='.git' -cvf - $(ls -A) | coder templates push -O coder memorycard --variables-file tmp.auto.tfvars.json -d -
```

But it would be nice if this was tracked and managed by the coderd_template instead.