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. The app will be pulled from upstream.

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

5. Parse all templates from local release.

kots template --license-file license.yaml --config-values config.yaml --local-path <path_to_release>

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!