add support for optional secrets using flag optional-secrets

[manherna]

Add support for optional secrets which are not required by default.

related to #152

[manherna]

Hi @arttor! It took me a while, but I found time to push this PR. What do you think? Does it suit the project scope? Does it lack anything?

[arttor]

hi, thank you for this proposal.
Can you please explain how optional secrets will be used?

I am asking only because i had different understanig based on our disucssion in #152.
My understanding was that:

1. User provides list of secret names as flag. These secrets should be created externally and not be a part of Helm chart.
2. Helmify will ignore listed secrets entirely and will not create any templates for these secrets
3. Helmify will find secret usages in other resoruces like Pod and replace it with a name of external secret, which will be stored in values.yaml as

   externalSecrets:
       <secret_name>: "<secret_name>"

[manherna]

Hi @arttor what do you think? Can this be merged?

[arttor]

sorry for not responding. But i am a bit struggling to understand the feature by looking at the code. Can you please explain what it does and what is the use-case?

[manherna]

Hi @arttor sorry, this went over my head.
The aim of this MR is to be able to decide wether a specific secret in the kustomize manifests is optional.
An optional secret, as per my view, is one that will be only created if its value is passed during installation and it is not null.

Imagine a registryCredentials secret. With this approach, the user installing the chart could decide to either install the chart with the value .Values.regisgtryCredentials.token and then the secret myhelmchart-registrycredentials would be created.
If, on the other hand, they would decide to leave that value empty or not define it, the secret myhelmchart-registrycredentials would not be created.

In my opinion this is useful because it allows users to either have the comfort of having a secret created upon install, or if they want they can define the secret themselves and maybe use something like ExternalSecrets to manage it.