chore(lockfileless): Made manifest kind hashable (#303)

Manifest kind needs to be hashable to be used in a `set()`. This PR adds
the `@dataclass(frozen=true)` decorator to it.

- [x] I ran `make setup && make` to update the generated code after
editing a `.atd` file (TODO: have a CI check)
- [x] I made sure we're still backward compatible with old versions of
the CLI.
For example, the Semgrep backend need to still be able to *consume* data
generated
	  by Semgrep 1.17.0.
See
https://atd.readthedocs.io/en/latest/atdgen-tutorial.html#smooth-protocol-upgrades

Author: SayyantR

semgrep_output_v1.atd

@@ -1817,7 +1817,7 @@ type output_format = [
 ]
 
 (* TODO: merge with Manifest_kind.ml *)
-type manifest_kind = [
+type manifest_kind <python decorator="dataclass(frozen=True)"> = [
   | RequirementsIn (* Manifest file for pip *)
   | PackageJson
   | Gemfile