Add more RDS metrics & labels.

[MrLotU]

No description provided.

[yourivandenberg]

The DatabaseClass dimension is not needed unless you want metrics for each DatabaseClass. See:
https://eu-west-1.console.aws.amazon.com/cloudwatch/home?region=eu-west-1#metricsV2:graph=~();query=~'*7bAWS*2fRDS*2cDatabaseClass*7d

vs

https://eu-west-1.console.aws.amazon.com/cloudwatch/home?region=eu-west-1#metricsV2:graph=~();query=~'*7bAWS*2fRDS*2cDBInstanceIdentifier*7d

[MrLotU]

I don't need them per database class, but I do need the database class for every instance. As far as I can see it's the only way to know what the total RAM allocation of a database is, which we need to calculate the connection pool size