If an enethe hits a duplicate from the Mirror Image spell, does it trigger the Tempest cleric’s Wrath of the Storm feature

Mirror Image states (p. 260 PHB)

Each time a creature targets you with an attack during the spell’s duration, roll a d20 to determine whether the attack instead targets one of your duplicates.

So:

1. a creature intends to target you,
2. you roll to determine if the creature in fact targets you OR one of your duplicates.

Sentinel states (p. 170 PHB)

When a creature within 5 feet of you makes an attack against a target other than you (and that target doesn’t have this feat), you can use your reaction to make a melee weapon attack against the attacking creature.

So:

1. if the creature in fact targets one of your duplicates then it hasn't targeted you; it does not need to hit the image, just target it
2. the image is an illusion so it does not have this feat

then you can use your reaction to make a melee weapon attack against the attacking creature. This is not an opportunity attack.

Sneak Attack states (p. 95 PHB)

Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.

You don’t need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isn’t incapacitated, and you don’t have disadvantage on the attack roll.

So,

1. if you haven't used sneak attack this turn
2. you have advantage (or an enemy of the target within 5 feet and no disadvantage; you could try to get your DM to agree that any images you have count - good luck with that)
3. you have a finesse melee weapon available

then this could be a Sneak Attack.

TL;DR

1. You can make an attack - this is not an Opportunity Attack.
2. If you meet the requirements, this may be a Sneak Attack.

When you use Wrath of the Storm with Thunderbolt Strike, the creature that attacked you is pushed back immediately. From the section on reactions:

If the reaction interrupts another creature’s turn, that creature can continue its turn right after the reaction.

The creature doesn't get to finish its turn, then get hit by your reaction - your reaction happens straight away, interrupting their turn. So if you use Wrath of the Storm + Thunderbolt Strike on the 1st attack of a Multiattack, the creature will be pushed back 10 feet.

Then, if it has movement remaining, it can move up to you and finish its Multiattack sequence. If it does not have enough movement to get back within reach of you, it will have to either end its turn without completing its Multiattack, or take the other attack(s) on a creature that is within its reach.