Adding this as a follow on to redis/redis#12466 to keep track of our efforts to provide a mapping of the structural changes (e.g. ZRANGE moving from flat array -> array of tuples) between RESP2 and RESP3

This work has already been started by @chayim and @uglide see this doc

We should have 2 bits of output in redis.io from this:

1. A collated RESP2->RESP3 migration guide calling out these changes
2. The impacted command pages should be updated to reflect the correct result structures

CC: @mgravell, @NickCraver, @oranagra, @itamarhaber