Apparently, some modules can afford deprecating command arguments
(something that was never done in Redis, AFAIK), so in order to represent
this piece of information, we added the `deprecated_since` field to redisCommandArg
(in symmetry to the already existing `since` field).
This commit adds `const char *deprecated_since` to `RedisModuleCommandArg`,
which is technically a breaking change, but since 7.0 was not released yet, we decided to let it slide