booleans that are written as strings cannot be parsed

### HCL Template
```hcl
# Place your HCL configuration file here
boolean_value = "true"
```

### Expected behavior
Elegantly handle "true" or "false" boolean strings

### Actual behavior
Stops decoding and gets an error:
At ##:##: root.boolean_value: unknown type *ast.LiteralType

### Steps to reproduce
1. Set a boolean value to "true" or "false" rather than true or false (no quotes)
2. Parse
3. Try to decode

### References

Start by reproducing the issue with the provided HCL configuration and follow the parsing and decoding entry points that produce the unknown type *ast.LiteralType error. Check how unquoted booleans are handled compared with quoted "true" and "false" values. Done means both boolean strings decode successfully without the reported error.

Written by the indexing model from the issue text.