Writable replicas now no longer use the data of expired keys. Expired keys
are deleted when lookupKeyWrite() is used, even on a writable replica.

This commit also sorts out the mess around the commands lookupKeyRead() and
lookupKeyWrite() so they now indicate what we intend to do with the key and
are not be affected by the command itself.

Multi-key commands like sunionstore, zinterstore, copy and sort with the
store option now use lookupKeyRead() for the keys they're reading from, but
with flags preserving the legacy behaviour (not touching keyspace hits/misses
counters, etc.).

Co-authored-by: yoav-steinberg <yoav@monfort.co.il>

Set current_client to AOF client during AOF loading.

Add an assert forbidding the WRITE flag in lookupKeyReadWithFlags.

Extra: Don't touch keys stats and LRU when determining ASK redirect.

…red key