Support setting whole section when option is unset

Docs sound like you can set a section by not setting option, but it didn't work previously, this fixes that.

Author: amosyuen

changelogs/fragments/10288-ini-file-fix-add-replace-whole-section.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - "ini_file - fixes adding or replacing a whole section (https://github.com/ansible-collections/community.general/pull/10288)."