Reduce diff for protovalidate/quickstart-es buf.gen.yaml

[timostamm]

In protovalidate/quickstart-es, start/buf.gen.yaml and finish/buf.gen.yaml differ quite a bit:

version: v2
+ clean: true
inputs:
  - directory: proto
plugins:
  - remote: buf.build/bufbuild/es:v2.5.1
    out: src/gen
+   opt:
+     - target=ts
+     - import_extension=js
    include_imports: true

This changes the diff to:

version: v2
clean: true
inputs:
  - directory: proto
plugins:
  - remote: buf.build/bufbuild/es:v2.5.1
    out: src/gen
    opt:
      - target=ts
      - import_extension=js
+   include_imports: true

Adding include_imports is almost always necessary to add with protovalidate and protobuf-es (so that the imported file buf/validate/validate_pb.ts is generated).

I don't believe it makes sense to switch from JavaScript to TypeScript to show how to use protovalidate, so I think we should generate ts right from the start. Similar for clean: true.