Use a composite index for alf_transaction id and commit_time_ms columns

By default the indexes for the table alf_transaction are:

idx_alf_txn_ctms for commit_time_ms
fk_alf_txn_svr for server_id

and the id uses a primary key.

It is suggested by a customer with a large database (about 490M rows in alf_node) that the NodeServiceCleanup maintenance job that runs:

... may benefit from a composite index containing alf_transaction's id and commit_time_ms columns (where commit_time_ms is first in the order otherwise this will likely be ineffective).

Currently when the query is run, it can take an hour to two hours to run. A composite index may help cut down this time significantly.