changefeedccl: add frontier history and visualizer

- Add a component that periodically snapshots the whole frontier and stores the last N of them in a ring buffer, and have it dump this as part of debug zips / on command.

- Add a visualizer tool/script that can parse that information to visualize both individual frontiers (which spans have made what progress, etc) and the collected timeline of them.

Together these can help us visualize how changefeed progress is made and potentially help diagnose issues.

Jira issue: CRDB-55068

Start by locating the changefeed frontier implementation and the existing debug-zip or command output paths. Then determine how frontier snapshots and their retention should connect to a visualizer tool or script. Done means the requested frontier history is captured and exposed, and individual frontiers plus their timeline can be visualized.

Written by the indexing model from the issue text.