See: https://forum.rclone.org/t/a-small-bug-in-rclone-documentation/51774

In this commit the source of the modtime got changed to the wrong object by accident

0b96713 webdav: add an ownCloud Infinite Scale vendor that enables tus chunked upload support

This reverts that change and fixes the integration tests.

This commit improves error handling in two specific scenarios:

* Missing Download Links: A 5-second delay is introduced when a download
  link is missing, as low-level retries aren't enough. Empirically, it
  takes about 30s-1m for the link to become available. This resolves
  failed integration tests: backend: TestIntegration/FsMkdir/FsPutFiles/
  ObjectUpdate, vfs: TestFileReadAtNonZeroLength

* Unrecoverable 500 Errors: The shouldRetry method is updated to skip
  retries for 500 errors from "idx.shub.mypikpak.com" indicating "no
  record for gcid." These errors are non-recoverable, so retrying is futile.

This ocurred whenever there were more than 100 files in the source due
to the output channel filling up.

The fix is not to use list.NewSorter but take more care to output the
dst objects in the same order the src objects are delivered. As the
src objects are delivered sorted, no sorting is needed.

In order not to cause another deadlock, we need to send nil dst
objects which is safe since this adjusts the termination conditions
for the channels.

Thanks to @jeremy for the test script the Go tests are based on.

Linkbox have started issuing 302 redirects on some of their PUT
requests when rclone uploads a file.

This is problematic for several reasons:

1. This is the wrong redirect code - it should be 307 to preserve the method
2. Since Expect/100-Continue isn't supported the whole body gets uploaded

This fixes the problem by first doing a HEAD request on the URL. This
will allow us to read the redirect Location and not upload the body to
the wrong place.

It should still work (albeit a little more inefficiently) if Linkbox
stop redirecting the PUT requests.

See: https://forum.rclone.org/t/linkbox-upload-error/51795
Fixes: #8606

Before this change, if not using shared key or SAS URL authentication
for the source, rclone gave this error

    ManagedIdentityCredential.GetToken() requires exactly one scope

when doing server side copies.

This was introduced in:

3a5ddfc azureblob: implement multipart server side copy

This fixes the problem by creating a temporary SAS URL using user
delegation to read the source blob when copying.

Fixes #8662