Change default RDS instance type to db.t3.small

[ryewilson]

Closes #68

The current default instance type is db.t2.small, but this is currently deprecated. This change makes it so that db.t3.small is used instead.

The deprecated status is shown at the bottom of the first table on this page

[casperbiering]

@oavdeev Do you have time to take a look at this please?

[acsbendi]

@ryewilson Don't you think that actually a db.t3.micro would be enough?

[ryewilson]

@ryewilson Don't you think that actually a db.t3.micro would be enough?

I changed it to db.t3.small because it was previously db.t2.small, and t3.small is the most similar replacement. I assume there was a reason that db.t2.small was originally used instead of db.t2.micro. Maybe @oavdeev can comment further.

[acsbendi]

@ryewilson Yes, I understand that. I would like to know the original justification for using db.t2.small rather than db.t2.micro too. We've been running Metaflow with a db.t3.micro for a couple of days and so far we haven't seen any issues.

[ryewilson]

@oavdeev Thank you, can you merge?

[ryewilson]

@oavdeev Can you merge if it's good to go?