chore: add gitignore for coder template build artifacts

- ignore tar.gz files (temporary build artifacts)
- ignore terraform state and lock files
- ignore override files

Author: mohsin-wiser

.coder/.gitignore

@@ -0,0 +1,19 @@
+# Build artifacts
+*.tar.gz
+template.tar.gz
+
+# Terraform state files
+*.tfstate
+*.tfstate.*
+.terraform/
+.terraform.lock.hcl
+
+# Crash log files
+crash.log
+crash.*.log
+
+# Override files
+override.tf
+override.tf.json
+*_override.tf
+*_override.tf.json