Limit total number of pods created by the controller

# Summary

Kubernetes clusters often max out with a number of scheduled running pods. For us, limiting this to 5k allow us to protect ourselves.

# Use Cases

Prevent broken clusters. Protect other cluster users.

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**Message from the maintainers**:

Impacted by this bug? Give it a 👍. We prioritise the issues with the most 👍.

Start by reviewing the issue and merged pull request #4892, including its discussion and changed behavior. Check whether the merged work addresses the requested five-thousand-pod limit and what remains, then identify the relevant controller entry point and tests before defining completion.

Written by the indexing model from the issue text.