Add PushDownDereferencesThroughMarkDistinct rule to optimizer

[losipiuk]

As spotted by @kasiafi PushDownDereferencesThroughMarkDistinct was missing from the list of rules.
Likely an omission.

[phd3]

😮

Is there an easy-to-add test (i.e. in TestDereferencePushDown) if we've identified issue with a particular query?

I'm not sure what is our general policy for e2e plan tests for optimizer rules, but that could've saved us here. Since the rule has a test, I'm fine with merging this as is.

[kasiafi]

@phd3 This was identified while inspecting code, so no ready test case. I think it would be worthy to add one.

[mosabua]

@losipiuk @kasiafi @phd3 is this still valid. Looks like a very quick change that might already be done actually. Could you close or update and merge please?

[losipiuk]

@losipiuk @kasiafi @phd3 is this still valid. Looks like a very quick change that might already be done actually. Could you close or update and merge please?

Oh - it was left behind :) Let me see if it is still valid

[colebow]

Does this have a tangible user impact / does it need a release note?

[losipiuk]

Does this have a tangible user impact / does it need a release note?

It can impact performance some obscure queries for which pushdown would not happen without hte change. But it is not anything substantial, and also would be super hard to percisly describe it in RN. Let's skip it.