Image Customizer: Make either one of split partitions format and output image format required

[amritakohli]

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 (./SPECS/LICENSES-AND-NOTICES/data/licenses.json, ./SPECS/LICENSES-AND-NOTICES/LICENSES-MAP.md, ./SPECS/LICENSES-AND-NOTICES/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

We want to allow user to extract just the partition files and not the image file itself. We also want the user to be able to extract the image and not partition files.
This change makes either one of the two flags, --output-split-partitions-format and --output-image-format, required to allow for this.
Previously, output image format was a required argument.

Change Log

• Add conditionals to make either one of the flags required.
• Documentation updated.

Does this affect the toolchain?

NO

Test Methodology

• Tested all cases locally: Neither flag mentioned. Output image format specified only. Output split partitions format specified only. Both specified.
  Error example:
  sudo go run ./imagecustomizer --build-dir ./build --image-file ~/core-2.0.20231115.vhdx --output-image-file ./out/image5.raw --config-file ~/config-3.yaml
  imagecustomizer: error: Either --output-image-format or --output-split-partitions-format must be specified.
  exit status 1