*: Move manifests to a saner location

[krnowak]

CI: http://jenkins.infra.kinvolk.io:8080/job/container/job/sdk/1149/cldsv/

This moves the manifests directory from sdk_container/.repo/manifests to the toplevel manifests directory. The location of manifests inside the SDK container is made a bit more consistent by moving it from /mnt/host/sources/.repo/manifests to /mnt/host/sources/src/scripts/manifests.

Other related PRs:

• mantle: sdk: Use new manifests location mantle#470
• flatcar-website: Use new location of manifests flatcar-website#282
• flatcar-demos: Use new manifests location flatcar-demos#7

Reasons:

• sdk_container/.repo/manifest is just a ridiculously obscure location for a file that sourced and checked everywhere.

• .repo is probably a leftover from Google's repo tool, which we don't use any more.

• I want /mnt/host/sources/ to stop being a mountpoint (this is where sdk_container directory is mounted).

  • I added (locally still, not filed a PR yet) a functionality to mount custom volumes with run_sdk_container but adding volumes to /host/mnt/sources/src makes a mess in the scripts repository. So this manifests directory move is a first step to avoid mounting sdk_container directory to /mnt/host/sources. We could instead mount coreos-overlay and portage-stable in /mnt/host/sources/src/third_party.
  • Maybe in future we could have /mnt/scripts as a mountpoint only, without this sources/src/third_party nonsense.

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)

  • no changelog added, that's not a user visible change

• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.

  • no surprises from this PR

[krnowak]

CI passed.

[github-actions]

Build action triggered: https://github.com/flatcar/scripts/actions/runs/6651965781