experiment with instance sizes for quicker RDS init

[setheliot]

• [ ] It still takes 15 minutes to create the databases and DMS instances. I’d like to experiment with instance sizes to see if we can get that faster without getting too crazy on instance size.

• [x] Use a parameter to specify the size of the DB instance. Have a default for lab participants.

Biggest delay is that it takes a snapshot -- small instance means small network, so this is slow. Maybe one of these can help?

(this was split off from https://github.com/setheliot/aws-well-architected-labs/issues/3

[setheliot]

example of recent provisioning with a db.t2.xlarge

Time	System notes
Sat, 05 Oct 2019 19:18:19 GMT	DB instance created
Sat, 05 Oct 2019 19:18:19 GMT	Applying modification to convert to a Multi-AZ DB Instance
Sat, 05 Oct 2019 19:26:32 GMT	Finished applying modification to convert to a Multi-AZ DB Instance
Sat, 05 Oct 2019 19:28:10 GMT	Monitoring Interval changed to 0
Sat, 05 Oct 2019 19:28:10 GMT	Performance Insights has been disabled
Sat, 05 Oct 2019 19:28:26 GMT	Backing up DB instance
Sat, 05 Oct 2019 19:30:29 GMT	Finished DB Instance backup
Sat, 05 Oct 2019 19:31:48 GMT	Finished updating DB parameter group

[setheliot]

https://github.com/setheliot/aws-well-architected-labs/pull/47

[setheliot]

Event	db.t2.large	db.m5.24xlarge	db.t3.2xlarge
----	----	----	----
DB instance created	0:00:00	0:00:00	0:00:00
Applying modification to convert to a Multi-AZ DB Instance	0:00:00	0:00:10	0:00:08
Finished applying modification to convert to a Multi-AZ DB Instance	0:08:13	0:07:02	0:07:04
Monitoring Interval changed to 0	0:01:38	0:01:05	0:01:19
Performance Insights has been disabled	0:00:00	0:00:00	0:00:00
Backing up DB instance	0:00:16	0:00:20	0:00:19
Finished DB Instance backup	0:02:03	0:02:02	0:03:16
Finished updating DB parameter group	0:01:19	0:01:20	0:01:08