Support disabling/enabling only read or write tag throttling

Right now, we have tooling in fdbcli to enable or disable automatic throttling. Now that we support read and write tag throttling, we should make this more granular and allow us to enable and disable each one independently.

Start with the existing automatic throttling enable and disable commands in fdbcli, then trace how read and write tag throttling are represented. Add independent controls for each throttling type and verify that enabling or disabling one does not change the other.

Written by the indexing model from the issue text.