feat!: support hashicorp/helm provider 3.x

[KOCEAN33]

What

Migrate the module to the hashicorp/helm provider 3.x API.

Why

helm provider 3.0 adopted the Terraform Plugin Framework and replaced the nested blocks with list/object attributes, in both the helm_release resource and the provider configuration. This module used the legacy dynamic "set" / dynamic "postrender" block form, so it does not work with helm >= 3.0. Closes #7.

Changes

• main.tf — convert set, set_sensitive, postrender from dynamic blocks to the attribute form:

  postrender    = try(var.argocd.postrender, null)
  set           = try(var.argocd.set, null)
  set_sensitive = try(var.argocd.set_sensitive, null)

  Values pass through from var.argocd, so the public argocd input shape is unchanged for callers already supplying set = [{ name, value }].
• versions.tf — raise the helm provider floor to >= 3.0.0.
• tests/complete — update provider "helm" to the v3 attribute form (kubernetes = { ... }) and remove the unused, undeclared provider "kubectl" block that blocked terraform init.
• README.md — regenerated provider/requirement version.

Breaking change

Requires helm provider >= 3.0.0. Consumers still on helm 2.x should stay on the 0.1.x line — see the < 3.0.0 cap in #11. Suggest releasing this as 0.2.0.

Verification

# root module
$ terraform init -backend=false && terraform validate
Success! The configuration is valid.   # helm 3.2.0

# tests/complete
$ terraform init -backend=false && terraform validate
Success! The configuration is valid.   # helm 3.2.0

DCO: commit signed off via git commit -s.