Add Helm manifest gen

[Trojan295]

Description

Changes proposed in this pull request:

• Add capact alpha manifest-gen implementation helm command
• Rename --override flag to --overwrite
• Add unit tests for the manifest generation code

Testing

You can use the following command to generate manifests for the bitnami/postgresql Helm chart:

go run cmd/cli/main.go alpha manifest-gen implementation helm cap.implementation.bitnami.postgresql.install postgresql --repo "https://charts.bitnami.com/bitnami" -i cap.interface.database.postgresql.install

Problems

1. If user provides an empty parameter value for a string, it will be interpreted as null, when evaluating values in workflow.
   The values of the parameters are transformed to strings in format:

   key: <@ additionalInput.key | default("some_default") @>
   # becomes, if user provides an empty string as value
   key:        # interpreted as null in YAML

   I couldn't find a way to make yaml.Marshal add double quotes to every string value so it would be ok.

2. If a key in Helm values.yaml contains a dot, then Jinja will have problem with interpreting it correctly. I'm not sure if this is a problem in Jinja as changing it to object[key] instead of object.key does not work also.

   # does not work
   annotations:
      prometheus.scrape: <@ additionalInput.annotations.prometheus.scrape @>
   
   # also does not work
   annotations:
      prometheus.scrape: <@ additionalInput.annotations["prometheus.scrape"] @>

Related issue(s)

Closes #417

[mszostok]

Overall, really nice work

It's awesome that you added test coverage and refactored code, it's more readable right now.

Regarding problem with escaping in jinja templating we can wait for our jinja sensei @lukaszo

[Trojan295]

I reopened the PR in #459, as I accidentally removed the branch from my fork...

edit: nvm

[pkosiec]

@Trojan295 FYI you could reopen the same pull request if you didn't create the new one 🙂 You can try closing the new one (#459) and reopening this, probably it would be easier to track post-review changes, but it's up to you.

[mszostok]

lgtm, just minor comments

[mszostok]

nit

Suggested change

	schema.Title = parentKeyPath[len(parentKeyPath)-1]
	schema.Title = strcase.ToCamel(parentKeyPath[len(parentKeyPath)-1])

[mszostok]

Suggested change

	from: "{{"{{"}}steps.prepare-parameters.outputs.artifacts.merged{{"}}"}}"
	from: "{{`{{steps.prepare-parameters.outputs.artifacts.merged}}`}}"

IMO it can be done in more readable way, simply replace

"{{"{{"}}

with

"{{`{{

(in the same way right brackets)

so from this

"{{"{{"}}steps.prepare-parameters.outputs.artifacts.merged{{"}}"}}"

you will get

"{{`{{steps.prepare-parameters.outputs.artifacts.merged}}`}}"