Better sub inputs handling (#193)

* Support for sub_inputs in extra plugins

* fix: properly handle lists as TOML arrays

- Updated the Jinja template to detect and serialize lists using |to_json,
  ensuring Telegraf interprets them correctly (e.g. names = ["item1","item2"]).
- Removed fallback logic for single items, so we consistently treat all sub_input
  values as lists of dictionaries.

---------

Co-authored-by: Michał Lisowski <mlisowski@sentient.ie>

templates/telegraf-extra-plugin.conf.j2

@@ -56,10 +56,16 @@
 {% endfor %}
 {% endif %}
 {% if item.value.sub_inputs is defined and item.value.sub_inputs is iterable %}
-{% for sub_input, config in item.value.sub_inputs.items() %}
-[[inputs.{{ item.value.plugin | default(item.key) }}.{{ sub_input }}]]
-{% for items in config %}
-    {{ items }}
+{% for sub_input_key, sub_input_list in item.value.sub_inputs.items() %}
+{% for block in sub_input_list %}
+[[inputs.{{ item.value.plugin | default(item.key) }}.{{ sub_input_key }}]]
+{% for param_key, param_value in block.items() %}
+{% if param_value is sequence and param_value is not string %}
+    {{ param_key }} = {{ param_value | to_json }}
+{% else %}
+    {{ param_key }} = "{{ param_value }}"
+{% endif %}
+{% endfor %}
 {% endfor %}
 {% endfor %}
 {% endif %}