Introduce a new more-block friendly syntax for specifying mounts with a new `mount` block type with the target as label:
```hcl
config {
image = "..."
mount {
type = "..."
target = "target-path"
volume_options { ... }
}
}
```
The main benefit here is that by `mount` being a block, it can nest blocks and avoids the compatibility problems noted in https://github.com/hashicorp/nomad/pull/9634/files#diff-2161d829655a3a36ba2d916023e4eec125b9bd22873493c1c2e5e3f7ba92c691R128-R155 .
The intention is for us to promote this `mount` blocks and quietly deprecate the `mounts` type, while still honoring to preserve compatibility as much as we could.
This addresses the issue in https://github.com/hashicorp/nomad/issues/9604 .
