Feature: kots template

[nvanthao]

What this PR does / why we need it:

It is currently difficult to debug templating error thrown by KOTS during install.

Which issue(s) this PR fixes:

Special notes for your reviewer:

This PR introduce new command kots template with 4 options to parse template.

1. Parse raw template directly from --data flag.

E.g.

kots template --license-file license.yaml --config-values config.yaml --data '{{repl ConfigOption "hostname" | ToUpper }}'

MYHOST

2. Parse template interactively. New REPL session will be created to parse template

kots template --license-file license.yaml --config-values config.yaml --interactive

3. Parse template by file

kots template --license-file license.yaml --config-values config.yaml <path_to_template>

4. Parse all templates in kotsKind directory, this behave similar to helm template where all files in kotsKind directory will be printed to stdout.

kots template --license-file license.yaml --config-values config.yaml 

Does this PR introduce a user-facing change?

New command line command `kots template`

Does this PR require documentation?

Yes

[CLAassistant]

All committers have signed the CLA.

[cbodonnell]

the rendered directory should already have the rendered helm templates, plain k8s manifests, and additional resources created by kustomize (pull secrets and any customer patches). i think we may be able to instead just iterate and print the files in that directory?

the kotskinds will not be in rendered, so i think what you have above this is good

[nvanthao]

Many thanks Craig! I've included rendered directory excluding kotsadm- files. However I think we should also run helm template on helm/ directory for HelmChart v2. What do you think?

[cbodonnell]

the rendered directory will already contain the helm template output in an all.yaml file for each HelmChart, so i think we can just iterate over all of the files there, including the kotsadm- files since those will ultimately be deployed along with everything else

[nvanthao]

gotcha! I've removed the helm template part. Please let me know how it goes!