add 'ksctl generate nstemplatetiers' command

[MatousJobanek]

based on the changes in host-operator repo and toolchain-common - see codeready-toolchain/toolchain-common#381

this PR adds a new command ksctl generate nstemplatetiers that takes a folder with tier templates (in the same format as we have in host-operator here: https://github.com/codeready-toolchain/host-operator/tree/master/deploy/templates/nstemplatetiers) and generates resulting TierTemplates and NSTemplateTiers in the out directory together with kustomization.yaml files.
In this way, Konflux team can move the definition of their tiers out of host-operator and manage them in infra-deployments via ArgoCD.

KUBESAW-60

For testing purposes, I copied the content of the appstudio tiers into test-resources folder

[mfrancisc]

Great Job 👍

I have only one minor question - is it intentional that the command creates also the source directory or should we just create the out-dir specified in the parameter?

I see that for example in this command:

/ksctl generate nstemplatetiers --source /Users/fmuntean/go/src/github.com/codeready-toolchain/host-operator/deploy/templates/nstemplatetiers/base --out-dir /tmp/basetemplates

the base folder is created in the output dir, even if not specifically required, but I guess it's fine.

Storing TierTemplate with name base-dev-1823953810-1823953810 in /tmp/basetemplates/base/tiertemplate-base-dev-1823953810-1823953810.yaml

[MatousJobanek]

@mfrancisc
Good question - the command groups the manifests in folders by tier name and it doesn't care if it's one tier or more of them. For the simplicity, I would keep it as it is.

[codecov]

Codecov Report

Merging #31 (d1ecc69) into master (cfee5c4) will decrease coverage by 0.16%.
The diff coverage is 62.35%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #31      +/-   ##
==========================================
- Coverage   65.72%   65.57%   -0.16%     
==========================================
  Files          40       41       +1     
  Lines        2028     2100      +72     
==========================================
+ Hits         1333     1377      +44     
- Misses        537      560      +23     
- Partials      158      163       +5     

Files	Coverage Δ
pkg/cmd/generate/generate.go	0.00% <0.00%> (ø)
pkg/cmd/generate/util.go	77.03% <78.57%> (+1.20%)	⬆️
pkg/cmd/generate/nstemplatetiers.go	55.35% <55.35%> (ø)