Add a function to append section

[QEDK]

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Similar to configparser in Python, we should have an option to append sections using a direct hashmap and string.

• append(Some(sectionname), HashMap to append) - If None, we append the section as-is (validate that it's a two-level hashmap), if Some(...), we create a hashmap with that section and add the entire section (need an error-check to ensure it's a flat hashmap).
• append_str(...) - Same behaviour as above, we run the underlying stuff through parse() and add some error checks.