Reimplement retry-interval when draining nodes

[omgrr]

This addresses #185 by re-adding the retryInterval when draining.

This also re-adds the retry-go package in order to do both the retry and the delay functionality. If there was another reason for removing it let me know!

Testing this on an actual cluster with setting the drain-interval to 30 seconds and the drain-timeout to 120 seconds I can see from the logs that there is the correct amount of time between retries.

time="2024-01-12T19:32:06Z" level=info msg="retrying drain, node <node name>"
time="2024-01-12T19:34:36Z" level=info msg="retrying drain, node <node name>"
# 2 minutes 30 seconds between retries