Make the image prefix configurable

[OisinJohnston2005]

This PR is resolving issue #4595, which requests the ability to configure the default prefix used when resolving image names into fully qualified urls, it asks for the ability to do so either by environment variable or command line argument, this PR implements both prioritising cli args and falling back to the environment variable and then the hard coded prefix.

In order to implement this I removed the ResolveToImageForCLI function since its approach of currying the default image prefix into the ResolveToImage function attribute on the RunnerOptions struct didn't allow Cobra to update the ImagePrefix on runtime.

Instead I opted to implement ResolveToImage as a method and added the ImagePrefix attribute which is updated by cobra whenever a command is run, if no prefix is provided it first checks for the environment variable KPT_IMAGE_PREFIX if set it will use that as the image prefix if not it will use ghcr.io/kptdev/krm-functions-catalog/

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[dosubot]

📄 Knowledge review

✏️ Suggested updates

3 page suggestions need review.

Page	Library	Status
_index /kpt/blob/main/documentation/content/en/book/04-using-functions/_index.md	kpt	⬆️ Pushed to this PR
_index /kpt/blob/main/documentation/content/en/reference/cli/fn/render/_index.md	kpt	⬆️ Pushed to this PR
_index /kpt/blob/main/documentation/content/en/reference/cli/fn/eval/_index.md	kpt	⬆️ Pushed to this PR

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[Copilot]

Pull request overview

This PR addresses #4595 by making the default prefix used to expand short KRM function image names configurable at runtime, via a new KPT_IMAGE_PREFIX environment variable and (for relevant commands) a --image-prefix CLI flag. It refactors the image-resolution logic so Cobra can update the configured prefix at execution time rather than relying on a curried function stored in options.

Changes:

• Added DefaultImagePrefix() (env var fallback) and refactored RunnerOptions to carry ImagePrefix plus a ResolveToImage method.
• Added --image-prefix flag wiring for fn render and fn eval.
• Updated command/test code to align with the RunnerOptions refactor and adjusted behavior for fn doc.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
thirdparty/cmdconfig/commands/cmdeval/cmdeval.go	Adds --image-prefix flag for fn eval and uses RunnerOptions.ResolveToImage method.
thirdparty/cmdconfig/commands/cmdeval/cmdeval_test.go	Updates expected RunnerOptions shape due to refactor (now includes ImagePrefix).
pkg/lib/runneroptions/runneroptions.go	Introduces env-var-based defaulting and replaces ResolveToImage function field with ImagePrefix + method.
pkg/fn/runtime/wasmtime_unsupported.go	Tweaks unsupported-wasmtime error message and adds linter suppression (needs follow-up).
commands/fn/render/cmdrender.go	Adds --image-prefix flag for fn render.
commands/fn/doc/cmdfndoc.go	Switches to using DefaultImagePrefix() when resolving images for fn doc.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 6 comments.

[liamfallon]

@OisinJohnston2005 Can you resolve the copilot comments please?