Increase the size of changelog and actionlog

The (uncompressed) changelog and actionlog size is currently 10MB and 2MB respectively.

On busy clusters (many concurrent chunk migrations and splits), I have seen the changelog window shrink to ~2 hours.

For diagnostic purposes it would be useful to increase the changelog and actionlog size to hold a longer time window.

Suggested sizes:

• changelog: 200 MB (20x)
• actionlog: 20 MB (10x, as it tends to be less subject to writes in a busy cluster)