shared/api/url: Fix double path encoding issue

[tomponline]

Go's net.URL requires Path to be populated with unencoded path and RawPath to be populated with the hint on how we want Path to be encoded.

This avoids double path encoding when calling url.EscapedPath(), which is used in url.String().

Fixes #12398

Before:

lxc storage volume create default tüdeldü
lxc storage show default
config:
  source: /var/lib/lxd/storage-pools/default
description: ""
name: default
driver: dir
used_by:
- /1.0/storage-pools/default/volumes/custom/t%25C3%25BCdeld%25C3%25BC

After:

lxc storage show default
config:
  source: /var/lib/lxd/storage-pools/default
description: ""
name: default
driver: dir
used_by:
- /1.0/storage-pools/default/volumes/custom/t%C3%BCdeld%C3%BC

Closes #12406