fix(pdk) proper __mode for 'kong.ctx' named contexts
fix(pdk) proper __mode for 'kong.ctx' named contexts

See `kong.global` module's `set_named_ctx` API. The third argument
(`key`) will be a plugin's configuration table. It is important not to
hold references to those configuration tables, as already observed
across many parts of the codebase.

Kong/kong,Kong/kong,Mashape/kong,Kong/kong