feat: Secrets under environments

[mumoshu]

Extracted from #59 (comment)

Enhance #253 to accept secrets: under each environment:

environments:
  production:
  values:
  - environments/production/values.yaml
  secrets:
  - environments/production/secrets.yaml

releases:
- name: myapp
  values:
  - values.yaml.gotmpl

So that contents of values.yaml and decrypted secrets.yaml are merged and then can be referenced from within values.yaml.gotmpl.

[Xtigyro]

@mumoshu If this is applied - will the secrets coming from HashiCorp Vault be suppressed too?

[mumoshu]

This feature is not about suppressing secrets from being printed. But yes, --suppress-secrets should prevent any k8s secret from being printed regardless of where the source is(vault, ssm, etc