fix exists command on slave

Bug was intoduced by redis#5021.

Before that commit, dbExists was used instead of
lookupKeyRead (which affects access time)

… replica (#8016)

The bug was introduced by #5021 which only attempted avoid EXIST on an
already expired key from returning 1 on a replica.

Before that commit, dbExists was used instead of
lookupKeyRead (which had an undesired effect to "touch" the LRU/LFU)

Other than that, this commit fixes OBJECT to also come empty handed on
expired keys in replica.

And DEBUG DIGEST-VALUE to behave like DEBUG OBJECT (get the data from
the key regardless of it's expired state)

… replica (redis#8016)

The bug was introduced by redis#5021 which only attempted avoid EXIST on an
already expired key from returning 1 on a replica.

Before that commit, dbExists was used instead of
lookupKeyRead (which had an undesired effect to "touch" the LRU/LFU)

Other than that, this commit fixes OBJECT to also come empty handed on
expired keys in replica.

And DEBUG DIGEST-VALUE to behave like DEBUG OBJECT (get the data from
the key regardless of it's expired state)

… replica (#8016)

The bug was introduced by #5021 which only attempted avoid EXIST on an
already expired key from returning 1 on a replica.

Before that commit, dbExists was used instead of
lookupKeyRead (which had an undesired effect to "touch" the LRU/LFU)

Other than that, this commit fixes OBJECT to also come empty handed on
expired keys in replica.

And DEBUG DIGEST-VALUE to behave like DEBUG OBJECT (get the data from
the key regardless of it's expired state)

(cherry picked from commit f8ae991)

fix exists command on slave