During working under SERVER-99138 it was noticed that ShardRegistry API does not provide enough information about the shard state.

For example:

When the config shard is started to be migrated to the dedicated config server, it's not possible to check if the shard in in "draining" mode.

Also another example after migration the special "config" shard id is still available via the call

ShardRegistry::getShard()

as it uses also

_configShardData.findShard(shardId) 

Then only one way to check if the config is the dedicated server to iterate through 

Grid::get(opCtx)->shardRegistry()->getAllShardIds(opCtx); 

and check if it contains "config" shard id.

as it uses directly 

_getData(opCtx)->getAllShardIds() 

ShardRegistry API should be enhance to provide common information about the shard state.

• Is the shard a "data shard"?
• Is the shard in "draining" mode?
• What type "config" is used
• etc.