config from .d/ is not loaded

[Ryan Hill]

When running do-release-upgrade, config items from the /etc/update-manager/release-upgrades.d/

More specifically, they are loaded initially to determine ubuntu flavor, but only MetaPkgs are used.

```
  File "/usr/bin/do-release-upgrade", line 133, in <module>
    m = MetaReleaseCore(useDevelopmentRelease=options.devel_release,
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/MetaRelease.py", line 104, in __init__
    self.flavor = get_ubuntu_flavor(cache=cache)
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/utils.py", line 408, in get_ubuntu_flavor
    pkg = get_ubuntu_flavor_package(cache=cache)
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/utils.py", line 428, in get_ubuntu_flavor_package
    meta_pkgs.extend(sorted(_load_meta_pkg_list()))
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/utils.py", line 416, in _load_meta_pkg_list
    parser = DistUpgradeConfig('/usr/share/ubuntu-release-upgrader')
  File "/usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeConfigParser.py", line 60, in __init__
```

However the config is loaded a second time in Core/MetaRelease.py and only /etc/update-manager/release-upgrades is used for config so items such as Prompt overrides in the .d directory are not found.

p.s. My initial goal was to override Prompt with Prompt=never under the .d directory

[Nick Rosbrook (enr0n)]

What version of Ubuntu are you trying this on?

[Ryan Hill (rthill91)]

I've seen the same behavior in 20.04, 22.04, and 22.10.

22.04 was where I initially ran into the issue.