Add OpenTofu, use by default for Terraform (#391)

Seems fairly straightforward to me, Terraform is no longer open-source,
OpenTofu is the compatible open-source successor, similar to the
Redis/Valkey situation.

Of course, if someone still prefers to use Terraform instead, they can
easily customize using:

```tf
(setf (alist-get 'terraform-mode apheleia-mode-alist) 'terraform)
```

We don't have a mechanism for allowing multiple formatters to be
registered for the same major mode, where later ones could be used if
earlier ones are not installed. That might be a nice addition.

2 files changed, 12 insertions, 0 deletions

diff --git a/test/formatters/samplecode/opentofu/in.tf b/test/formatters/samplecode/opentofu/in.tf
new file mode 100644
index 0000000..7fd0456
--- /dev/null
+++ b/test/formatters/samplecode/opentofu/in.tf
@@ -0,0 +1,6 @@
+    resource "google_sql_user" "user" {
+  name              = "camunda"
+  instance =google_sql_database_instance.camunda-db.name
+
+            password       ="futurice"
+      }
diff --git a/test/formatters/samplecode/opentofu/out.tf b/test/formatters/samplecode/opentofu/out.tf
new file mode 100644
index 0000000..ca64220
--- /dev/null
+++ b/test/formatters/samplecode/opentofu/out.tf
@@ -0,0 +1,6 @@
+resource "google_sql_user" "user" {
+  name     = "camunda"
+  instance = google_sql_database_instance.camunda-db.name
+
+  password = "futurice"
+}