feat(template): support template-less image variant selection

[Nachiket-Roy]

Description

This PR adds support for image variants (for example, Ubuntu Minimal or Debian NoCloud) without introducing additional template files such as ubuntu-minimal.yaml or debian-nocloud.yaml.

A new variant field is added to image entries, allowing users to select specific image variants dynamically with the existing --set flag.

To preserve the current behavior, standard/server images are listed before minimal variants, ensuring that default template usage continues to select standard images.

How to use

Start Ubuntu 24.04 Minimal:

llimactl start --image-variant=minimal template:ubuntu-24.04

Start Debian 12 NoCloud:

limactl start --image-variant=nocloud template:debian-12

Tests

Added TestDefaultSelectedImageIsStandard to verify that standard images remain the default selection by ensuring they are ordered before minimal variants.

Fixes #5153
Fixes #5158

[AkihiroSuda]

--set '.images = [.images[] | select(.variant == "minimal")]' \

There should be --image-variant=STRING in

lima/cmd/limactl/editflags/editflags.go

Line 99 in 4d1c1b2

func RegisterCreate(cmd *cobra.Command, commentPrefix string) {

[Copilot]

Pull request overview

Adds first-class support for selecting OS image “variants” (e.g., Ubuntu minimal, Debian nocloud) without multiplying template files, by tagging image entries with a variant and enabling CLI-based filtering while preserving existing default image selection behavior.

Changes:

• Add variant to limatype.Image and propagate acceptance of the field through driver config validation.
• Introduce --image-variant flag (implemented via yq expression) to select a specific image variant at instance creation.
• Update Ubuntu/Debian image catalogs to include variant-tagged entries and add tests to validate unmarshalling and default ordering.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
templates/_images/ubuntu-26.04.yaml	Adds variant: server entries and introduces minimal variant images (with fallback).
templates/_images/ubuntu-24.04.yaml	Adds variant: server entries and introduces minimal variant images (with fallback).
templates/_images/ubuntu-22.04.yaml	Adds variant: server entries and introduces minimal variant images (amd64).
templates/_images/debian-13.yaml	Tags existing images as genericcloud/generic and adds nocloud variant images (with fallback).
templates/_images/debian-12.yaml	Tags existing images as genericcloud/generic and adds nocloud variant images (with fallback).
pkg/limayaml/defaults_test.go	Adds tests for variant unmarshalling and default image ordering in templates.
pkg/limatype/lima_yaml.go	Extends Image type to include Variant.
pkg/instance/start.go	Enforces “stick to the first variant for the target arch” during image download attempts.
pkg/driver/wsl2/wsl_driver_windows.go	Allows Variant in WSL2 image validation/unknown-field filtering.
pkg/driver/vz/vz_driver_darwin.go	Allows Variant in VZ image validation/unknown-field filtering.
cmd/limactl/editflags/editflags.go	Adds --image-variant flag and generates yq to filter .images by variant.

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