feat(rds): add public command to generate report of publicly exposed RDS instances

[clok]

added the gw-aws-audit rds public command

Produces a report that displays a list RDS servers that are configured as Publicly Accessible.
The report contains:

DB INSTANCE:
    - Name of the instance
ENGINE:
    - RDS DB engine
SECURITY GROUPS:
    - Security Group ID
    - Security Group Name
    - Inbound Port
    - CIDR rules applied to the Port

Example output

┌─────────────────────────┬───────────────────┬──────────────────────────────────────────────────────────────────────────────────────────┐
│ DB INSTANCE             │ ENGINE            │ SECURITY GROUPS                                                                          │
├─────────────────────────┼───────────────────┼──────────────────────────────────────────────────────────────────────────────────────────┤
│ metadata-db-1234        │ postgres          │ sg-1234589313123    airflow-metadb-prod-v2-sg    5432                                    │
│                         │                   │                                                                                          │
│                         │                   │            10.176.50.0/24       10.176.51.0/24       10.176.52.0/24        10.176.0.0/16 │
│                         │                   │           10.176.1.233/32                                                                │
│                         │                   │                                                                                          │
│ ab-prod-db              │ aurora-postgresql │ sg-ac67ac8a    rds-launch-wizard-28    5432                                              │
│                         │                   │                                                                                          │
│                         │                   │             10.176.0.0/16                                                                │
│                         │                   │                                                                                          │
├─────────────────────────┼───────────────────┼──────────────────────────────────────────────────────────────────────────────────────────┤
│ DB INSTANCES            │ 2                 │                                                                                          │
└─────────────────────────┴───────────────────┴──────────────────────────────────────────────────────────────────────────────────────────┘

[mrlannigan]

[clok]

I know...... I know. It's something. The go community prefers this.