ImageCustomizer: Implement new MIC Overlays APIs.

[liulanze]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./LICENSES-AND-NOTICES/SPECS/data/licenses.json, ./LICENSES-AND-NOTICES/SPECS/LICENSES-MAP.md, ./LICENSES-AND-NOTICES/SPECS/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

---

Summary

What does the PR accomplish, why was it needed?

This PR restructures the MIC Overlays APIs, optimizing the process by transitioning from relying on the initrd module script for enabling overlays to leveraging the fstab file. The changes streamline the Overlay feature, making it more generic and easier for users to configure and use.

Does this affect the toolchain?

NO

Associated issues

• Internal User Story Tracking

Test Methodology

• Local build:
• Used overlays field from the config file:

  overlays:
    - lowerDirs:
      - /etc
      upperDir: /var/overlays/etc/upper
      workDir: /var/overlays/etc/work
      mountPoint: /etc
      isRootfsOverlay: true
      mountDependencies: 
      - /var
    - lowerDirs:
      - /media
      - /home
      upperDir: /overlays/media/upper
      workDir: /overlays/media/work
      mountPoint: /media

• Print of df -h:

root [ /home/test ]# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        4.0M     0  4.0M   0% /dev
tmpfs           851M     0  851M   0% /dev/shm
tmpfs           341M  620K  340M   1% /run
tmpfs           4.0M     0  4.0M   0% /sys/fs/cgroup
/dev/sda3       1.9G  380M  1.4G  22% /
/dev/sda4       2.0G  193M  1.7G  11% /var
overlay         2.0G  193M  1.7G  11% /etc
tmpfs           851M     0  851M   0% /tmp
overlay         1.9G  380M  1.4G  22% /media
/dev/sda2        89M   32M   51M  38% /boot
/dev/sda1       8.0M  2.3M  5.7M  29% /boot/efi
tmpfs           171M     0  171M   0% /run/user/1000

• Print of fstab:

root [ /home/test ]# cat /etc/fstab
PARTUUID=a48afb5e-98d8-4910-ab67-ca790c6d8abc / ext4 defaults 0 1
PARTUUID=68e8263e-d932-4e98-87c1-f8e3e929a8e1 /boot ext4 defaults 0 2
PARTUUID=6282d628-3af5-4981-bd41-49f6057ab664 /boot/efi vfat umask=0077 0 2
PARTUUID=53b61c5f-4ebb-4ee7-847e-feb46ef5ffb9 /var ext4 defaults,x-initrd.mount 0 2
overlay /etc overlay lowerdir=/sysroot/etc,upperdir=/sysroot/var/overlays/etc/upper,workdir=/sysroot/var/overlays/etc/work,x-systemd.requires=/sysroot/var,x-initrd.mount,x-systemd.wanted-by=initrd-fs.target 0 0
overlay /media overlay lowerdir=/media:/home,upperdir=/overlays/media/upper,workdir=/overlays/media/work 0 0

[cwize1]

It would probably be good to also exclude tabs, newlines, colons, and commas to help avoid the path values from messing up the fstab file's formatting.

strings.ContainsAny could be handy for this.

Also, if you could also use validatePath for MountPoint.Path that would be greatly appreciated.

[liulanze]

Added, please check.

[cwize1]

It would probably be good to also exclude tabs and newlines.

Also, if you could apply the same check to MountPoint.Options that would be greatly appreciated.

[liulanze]

Added, please check.