Auto complete function images for eval command

[phanimarupaka]

This PR improves the discoverability of functions by providing tab completion for function images in the catalog available at https://catalog.kpt.dev/ (https://catalog.kpt.dev/catalog.json). Latest version for the image is suggested.

$ kpt fn eval -i [tab]
apply-setters:v0.1          fix:v0.2                    list-setters:v0.1           set-labels:v0.1             starlark:v0.2             
create-setters:v0.1         gatekeeper:v0.2             search-replace:v0.2         set-namespace:v0.1          upsert-resource:v0.1      
ensure-name-substring:v0.1  kubeval:v0.1                set-annotations:v0.1        set-project-id:v0.1 

$ kpt fn doc -i [tab]
apply-setters:v0.1          fix:v0.2                    list-setters:v0.1           set-labels:v0.1             starlark:v0.2             
create-setters:v0.1         gatekeeper:v0.2             search-replace:v0.2         set-namespace:v0.1          upsert-resource:v0.1      
ensure-name-substring:v0.1  kubeval:v0.1                set-annotations:v0.1        set-project-id:v0.1 

cc @Pitta @mikebz @grmoon

[Pitta]

excitement intensifies

[mikebz]

LGTM, thanks for adding the test.

@mengqiy is the spec for the catalog JSON defined somewhere? Could be interesting for @natasha41575 and @yuwenma to examine eventually and figure out how to build in similar functionality into kustomize.

@bgrant0607 was interested in auto complete for functions, but I am not sure if there was an issue for it.

[mikebz]

found the relevant issue and comments: #2344
fn doc issue by @frankfarzan #2009

[droot]

We should use https://pkg.go.dev/golang.org/x/mod/semver for the comparison.

[mengqiy]

is the spec for the catalog JSON defined somewhere?

It is defined in go/kpt-fn-metadata. It is used in the site generation script: https://github.com/GoogleContainerTools/kpt-functions-catalog/blob/master/scripts/generate_catalog/generate_catalog.go#L74-L98