Experiment is no longer required, the new method will be released without an experiment and without a toggle

Main PR is: #21398

**This is just the protobuf changes for the PR #21398

Moved `UploadFileRequest` from `provisionerd.proto` -> `provisioner.proto`.

Renamed to `FileUpload` because it is now bi-directional.

This **is backwards compatible**. I tested it to confirm the payloads are identical.  Types were just renamed and moved around.

```golang
func TestTypeUpgrade(t *testing.T) {
	t.Parallel()

	x := &proto2.UploadFileRequest{
		Type: &proto2.UploadFileRequest_ChunkPiece{
			ChunkPiece: &proto.ChunkPiece{
				Data:         []byte("Hello World!"),
				FullDataHash: []byte("Foobar"),
				PieceIndex:   42,
			},
		},
	}

	data, err := protobuf.Marshal(x)
	require.NoError(t, err)

	// Exactly the same output
	// EhgKDEhlbGxvIFdvcmxkIRIGRm9vYmFyGCo= on `main`
	// EhgKDEhlbGxvIFdvcmxkIRIGRm9vYmFyGCo= on this branch
	fmt.Println(base64.StdEncoding.EncodeToString(data))
}
```


# What this does

This allows provisioner daemons to download files from `coderd`'s `files` table. This is used to send over cached module files and prevent the need of downloading these modules on each workspace build.