helm: add support for the K8S_ envvars (#319)

Add support for:

- K8S_AUTH_HOST
- K8S_AUTH_API_KEY
- K8S_AUTH_VERIFY_SSL
- K8S_AUTH_SSL_CA_CERT

This commit also refactor the way we pass K8S related configuration to `helm`:

All the calls are now done in a new module_utils module (`helm.py`).
The handling of the `kube_*` variables has also been moved in this new
module.

We need https://github.com/helm/helm/pull/8622 to be able to ignore the
certificate validation. As a workaround, the generate a temporary
kubeconfig configuration file.

Closes: #279

plugins/doc_fragments/helm_common_options.py

@@ -31,4 +31,29 @@ options:
       - If the value is not specified in the task, the value of environment variable C(K8S_AUTH_KUBECONFIG) will be used instead.
     type: path
     aliases: [ kubeconfig_path ]
+  host:
+    description:
+    - Provide a URL for accessing the API. Can also be specified via C(K8S_AUTH_HOST) environment variable.
+    type: str
+    version_added: "1.2.0"
+  api_key:
+    description:
+    - Token used to authenticate with the API. Can also be specified via C(K8S_AUTH_API_KEY) environment variable.
+    type: str
+    version_added: "1.2.0"
+  validate_certs:
+    description:
+    - Whether or not to verify the API server's SSL certificates. Can also be specified via C(K8S_AUTH_VERIFY_SSL)
+      environment variable.
+    type: bool
+    aliases: [ verify_ssl ]
+    default: True
+    version_added: "1.2.0"
+  ca_cert:
+    description:
+    - Path to a CA certificate used to authenticate with the API. The full certificate chain must be provided to
+      avoid certificate validation errors. Can also be specified via C(K8S_AUTH_SSL_CA_CERT) environment variable.
+    type: path
+    aliases: [ ssl_ca_cert ]
+    version_added: "1.2.0"
 '''