s3 key sensor (sync version) has bad memory footprint

[dstandish]

Body

It currently loads all keys into memory. This is not necessary and, on the wrong bucket, can takedown the worker.

We saw this (and fixed) with the async version some time ago #40473.

But the sync version needs to be fixed.

Committer

• I acknowledge that I am a maintainer/committer of the Apache Airflow project.

[jroachgolf84]

I'm going to pick this one up.

[rahul1360]

Hi, @jroachgolf84 I'd like to contribut could you assign a issues ? This is myfirst time, so could you help me how to do that?