Update the cdc technical overview for new changefeed work distribution

[katmayb]

Fixes DOC-10675

Recently, the changefeed job planning was updated so that the work is distributed evenly across replicas in the cluster. This is on by default in v24.1+ and by enabling a cluster setting in v23.2 and v23.1.

This PR updates the How a changefeed works page, between v23.1–v24.2. In the earlier versions, there is a note added to the description to describe the new cluster setting. In 24.1+, this PR updates in the description in-line of how the changefeed work is assigned.

Also, updates the diagram in v24.1+ so that we are distributing work across all replicas (including leaseholders).