Support HTTP redirects for non-collection resources

[jwodder]

When a client GETs a blob asset or Zarr entry, the code currently "proxies" the request inefficiently by making a request for the actual resource on S3 and returning an fsspec IO object for use by wsgidav. Such GET requests should instead be responded to with HTTP redirects to the actual resources on S3.

Blocked by need for redirect support in wsgidav: mar10/wsgidav#311

• If wsgidav fails to add the necessary features, alternative ways to get redirect support include:
  • Fork wsgidav and add the features ourselves
    • @jwodder would rather not do this.
  • Find another Python WebDAV server library/framework that does support redirects
  • Write our own WebDAV server from (relatively speaking) scratch
    • If it came down to this, @jwodder would prefer to do it in Rust.