refactor: remove prefix "rw_" in session variables

[xxchan]

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What's changed and what's your intention?

Remove prefix "rw_" in session variables. fix #13265

Previous variables are still kept as aliases.

All changed variables:

• rw_implicit_flush
• rw_batch_enable_lookup_join
• rw_batch_enable_sort_agg
• rw_streaming_enable_delta_join
• rw_streaming_enable_bushy_join
• rw_streaming_allow_jsonb_in_stream_key
• rw_enable_join_ordering
• rw_enable_two_phase_agg
• rw_force_two_phase_agg
• rw_enable_share_plan
• rw_force_split_distinct_agg
• rw_streaming_over_window_cache_policy
• rw_enable_shared_source

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[BugenZhao]

Cool

[tabVersion]

can you also summarize the naming convention?

[xxchan]

Personally, I prefer the ones without RW_ prefix, because most session variables are specific to RW, and we don't plan to port many session variables from PG.

As for STREAMING/BATCH, I think it's optional and depends on the specific variables.

Originally posted by @fuyufjh in #13265 (comment)