Report configured chunk size in collectionBalancerStatus

The chunk size for a specific collection is calculated according to the following rules in order of precedence:

1. The collection specific chunk size maxChunkSizeBytes field in config.collection if set
2. The global chunk size setting in config.settings.chunkSize if set
3. The default global chunk size setting

So currently it is not straightforward for a user checking which is the currently configured chunk size setting for a specific collection. 
My proposal is to expose such information in the collectionBalancerStatus output, taking into account the 3 rules listed above.