S3 component shouldn't need trailing / on PROPFIND requests

[jhiemstrawisc]

At the moment, failure to include a trailing / on PROPFIND requests to the S3 backend results in a "no such file or directory" without sending any requests upstream to the S3 endpoint.

$ curl -v -X PROPFIND http://localhost:8443/my-prefix

> PROPFIND /my-prefix HTTP/1.1
> Host: localhost:8443
> User-Agent: curl/7.76.1
> Accept: */*
> 
< HTTP/1.1 404 Not Found
< Connection: Close
< Server: XrootD/v5.7.1
< Content-Length: 55
< 
Unable to locate /my-prefix; no such file or directory

Whereas including the trailing / reaches the known 403 on PROPFINDs after forwarding the request to the upstream S3 endpoint:

$ curl -v -X PROPFIND http://localhost:8443/my-prefix/
> PROPFIND /my-prefix/ HTTP/1.1
> Host: localhost:8443
> User-Agent: curl/7.76.1
> Accept: */*
> 
< HTTP/1.1 403 Forbidden
< Connection: Close
< Server: XrootD/v5.7.1
< Content-Length: 54
< 
Unable to locate /my-prefix/; operation not permitted

Existing 403 bug notwithstanding, I think these two cases should be treated the same, and we should handle adding the trailing / internally for these requests.

[jhiemstrawisc]

Closed by #58