`%paths` to `warm-up-command` does not include repo root, but should

[philipmw]

Suppose my file://rustic.toml looks like this:

[repository]
repository = "opendal:s3"
repo-hot = "opendal:s3"
warm-up-command = "warmup-s3-archives %paths"
warm-up-batch = 1000

[repository.options]
endpoint = "s3.dualstack.us-west-2.amazonaws.com"
region = "us-west-2"
root = "/rustic"

When I try to restore this data, the warmup-s3-archives command receives input arguments like this:
data/03/03dc1178e4e54f69beaf35dd9d4256a5a600e9fa3452b9db80bd649938923e67

But the correct S3 object key is:
rustic/data/03/03dc1178e4e54f69beaf35dd9d4256a5a600e9fa3452b9db80bd649938923e67.

This issue prevents restores from cold storage when a non-empty root is set.

We need to update the warmup logic to include the root when constructing paths.

(I will work on fixing this unless someone else wants to.)