Semantic versioning constraints for function images

[mozesl-nokia]

Closes #4383

It is now possible to provide semantic version constraints in a new tag field based on the using the spec of https://github.com/Masterminds/semver. kpt fn eval is also supported with a new --tag flag.

I've also added documentation for the feature, including CLI.

Fixed mdtogo generation as well.

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[Copilot]

Pull request overview

Adds semantic version tag constraints for Kptfile pipeline functions and kpt fn eval, resolving to the highest matching remote OCI tag using the Masterminds semver constraint spec.

Changes:

• Introduces tag on pkg/api/kptfile/v1.Function and threads it through function execution (including new kpt fn eval --tag support).
• Implements remote tag listing + semver constraint resolution (regclient + Masterminds/semver) with unit tests.
• Updates docs and e2e testdata/expectations (including KRM_FN_RUNTIME env var naming and regenerated CLI docs).

Reviewed changes

Copilot reviewed 27 out of 32 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
thirdparty/cmdconfig/commands/cmdeval/cmdeval.go	Adds --tag flag to kpt fn eval runner wiring.
pkg/test/runner/runner.go	Passes --tag through test runner to kpt fn eval.
pkg/test/runner/config.go	Adds tag to eval test case config schema.
pkg/api/kptfile/v1/types.go	Adds Function.Tag field and updates controller-gen directive.
main.go	Updates mdtogo go:generate inputs/paths for CLI docs generation.
internal/fnruntime/tag_resolution.go	New tag constraint resolution logic (semver + remote tag listing).
internal/fnruntime/tag_resolution_test.go	Unit tests for tag filtering/sorting and resolution behavior.
internal/fnruntime/runner.go	Threads Function.Tag into container runtime execution.
internal/fnruntime/container.go	Adds regclient-based tag lister and resolves image tag before container execution.
internal/docs/generated/overview/docs.go	Regenerated overview docs output (now missing CliShort).
internal/docs/generated/fndocs/docs.go	Regenerated function command docs including --tag documentation.
internal/docs/generated/rpkgdocs/docs.go	Removes generated rpkg docs output.
internal/docs/generated/repodocs/docs.go	Removes generated repo docs output.
go.mod	Adds semver + regclient deps; bumps cobra; indirect dep updates.
go.sum	Adds/updates checksums for new/updated dependencies.
e2e/testdata/fn-render/image-pull-policy-if-not-present/.expected/setup.sh	Updates expected env var usage to KRM_FN_RUNTIME.
e2e/testdata/fn-render/image-pull-policy-always/.expected/setup.sh	Updates expected env var usage to KRM_FN_RUNTIME.
e2e/testdata/fn-render/default-runtime/.expected/exec.sh	Updates expected env var usage to KRM_FN_RUNTIME.
e2e/testdata/fn-render/basicpipeline-semver/resources.yaml	New e2e package resources for semver-tag pipeline test.
e2e/testdata/fn-render/basicpipeline-semver/Kptfile	New e2e Kptfile using tag constraints for pipeline functions.
e2e/testdata/fn-render/basicpipeline-semver/.krmignore	Ignores .expected in new e2e test package.
e2e/testdata/fn-render/basicpipeline-semver/.expected/diff.patch	Expected output for new semver-tag pipeline test.
e2e/testdata/fn-render/basicpipeline-semver/.expected/config.yaml	Expected config for new semver-tag pipeline test.
e2e/testdata/fn-eval/simple-function-with-tag/resources.yaml	New e2e resources for fn eval with --tag.
e2e/testdata/fn-eval/simple-function-with-tag/.krmignore	Ignores .expected in new e2e test package.
e2e/testdata/fn-eval/simple-function-with-tag/.expected/diff.patch	Expected output for new fn eval --tag test.
e2e/testdata/fn-eval/simple-function-with-tag/.expected/config.yaml	Expected config for new fn eval --tag test.
e2e/testdata/fn-eval/image-pull-policy-if-not-present/.expected/setup.sh	Updates expected env var usage to KRM_FN_RUNTIME.
e2e/testdata/fn-eval/default-runtime/.expected/exec.sh	Updates expected env var usage to KRM_FN_RUNTIME.
documentation/content/en/reference/cli/fn/render/_index.md	Updates docs to use KRM_FN_RUNTIME.
documentation/content/en/reference/cli/fn/eval/_index.md	Documents --tag flag behavior.
documentation/content/en/book/04-using-functions/_index.md	Documents new tag field semantics with examples.

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[Copilot]

Pull request overview

Copilot reviewed 28 out of 32 changed files in this pull request and generated 7 comments.

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[liamfallon]

Looks good, just one or two small things.

[Copilot]

Pull request overview

Copilot reviewed 29 out of 33 changed files in this pull request and generated 2 comments.

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