Read terraform version from a .terraformrc file

Instead of hard coding the version in the workflow, it would be nice to have it read it from a file similar to how [`actions/setup-node@v3`](https://github.com/actions/setup-node) reads from `.nvmrc`

```yaml
- name: Setup node
uses: actions/setup-node@v3
with:
node-version-file: '.nvmrc'
```

Something like this perhaps ?

```yaml
- uses: actions/checkout@v3
- uses: hashicorp/setup-terraform@v2
with:
terraform_version_file: '.terraformrc'
```