ipip-0288 lacking etag clarity

[SgtPooki]

running conformance tests for @helia/verified-fetch results in the following error:

{
  "Time":"2025-02-11T09:07:30.674466-06:00",
  "Action":"output",
  "Package":"Gateway Tests",
  "Test":"TestTar/GET_TAR_with_format=tar_and_extract/Header_Etag",
  "Output":"        Error: Header 'Etag' expect to find substring 'W/\"bafkreialihlqnf5uwo4byh4n3cmwlntwqzxxs2fg5vanqdi3d7tb2l5xkm.x-tar', got '\"bafkreialihlqnf5uwo4byh4n3cmwlntwqzxxs2fg5vanqdi3d7tb2l5xkm.tar\"'\n"
}

However, there is no clarification on etag headers in the tar-response spec. We should link to https://github.com/ipfs/specs/blob/f504d048c227142e4bbdddbe8cc7ab5500c56a1d/src/http-gateways/path-gateway.md?plain=1#L410

Additional question(s):

1. Should tar responses only include etag ending in x-tar, or only when it's a weak etag?