Create Indexes on DateTime Fields on the Instance Model

[KipSigei]

Adding an index to the DateTimeFields on the Instance Model would improve performace when doing a sort on the logger instance table. This is because the logger_instance table has millions of records and currently without indexing the database performance is greatly impacted when a user does a sort operation with the date_modified field.

[alepietrobon]

@ukanga , @KipSigei suggested that for this to be tested, we might want to test it on a preview server with large scale, even if for a short time.
One way to achieve this would be to increase the RDS size for the Ona Data Stage server for a short period (a week), so we can create a duplicate of production (or something close to it) to check the impact of indexing on reads and writes.
Is this something you'd be ok with?