Add basic Postgres support

[autero1]

Add basic support for PostgreSQL. Includes adding the following capabilities

• [x] Basic information including name, tier, activation policy
• [x] Public IP with IP restrictions
• [x] Disk options (auto resizing, size, type)
• [x] Maintenance schedule
• [x] Backup schedule
• [x] Default db and user
• [x] Location preference
• [x] Custom labels

Includes #21