2.0: a few hours of work

General:
- Few small internal simplifications
- Cache-Control header based on the maximum age acceptable (already in
- config for health checks).

Per endpoint:
- /rds/all (new): RDS instances endpoint
- /iam/users (new): more verbose IAM endpoint
- /ec2/all (new): simpler, faster EC2 instances endpoint with all machines per AZ
- /ec2/sg (recent and yet to be documented): restructured for per-AZ