one must imagine Sisyphus happy

This is mvp which reuses http header logic from serveFile, plus custom
content-disposition to ensure browsers dont render garbage

This is PoC implementation that returns CAR as a chunked stream.
It does not set cache-control nor it has content-length.

TBD if we want/can have these things.

- extracted file-like content type responses to separate .go files
- Accept HTTP header with support for application/vnd.ipld.* types
  (TBD, we did not register them yet, so for illustration purpose only)

Include block and car in unixfs_get_latency_seconds for now,
so we keep basic visibility into gateway behavior until better metrics
are added by #8441

.raw may be handled by something, depending on OS, and .bin
seems to be universially "binary file" across all systems:
https://en.wikipedia.org/wiki/List_of_filename_extensions_(A%E2%80%93E)

This test uses official CARv1 fixture from
https://ipld.io/specs/transport/car/fixture/carv1-basic/

The CAR has two dag-cbor roots, and we use one of them, which represents
a nice DAG with both dag-cbor, dag-pb and raw blocks

#8758 (comment)

#8758 (comment)

- Moved UnixFS response handling to gateway_handler_unixfs*.go files.
- Removed support for X-Ipfs-Gateway-Prefix (Closes #7702)

#8758 (comment)

- removed dead code after X-Ipfs-Gateway-Prefix is gone
  (#7702)
- escaped special characters in content paths returned with http.Error
  making them both safer and easier to reason about (e.g. when invisible
  whitespace unicode is copied)

#8758 (comment)
lidel needs some sleep