Update repl connection instructions for data-retention.adoc

[denislemire]

• Server >= 4.8 no longer includes lein client in the front-end container
• Need to use a port forward and docker container instead.

Description

Changes repl connection instructions to use a kubectl port forward and a docker container for the lein client

Reasons

Server >= 4.8 no longer includes a lein client inside the container image so current instructions will not work

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