[WIP] Feature/db interface

[kellrott]

Starting to mock out what an actual server would need.

Work done:

• Abstract DB interface that would allow the DRS service handler connect to multiple backends
• Simple in memory database driver
• Simple AWS S3 URL signer, uses standard global AWS credentials to manage access (for testing development)
• Refactoring commands to use Cobra ( https://github.com/spf13/cobra ) for organization
• Switched openapi-generator from go-gin-server to go-server, because the latter has more options (directory output and module names) for code generation

To be done:

• Postgres DB driver
• Authentication module and way to connect it to DB and URL managers
• URL manager that connects to Vault for credentials
• Complete implementation of the DRS specification
• Robust config system that allows users to deploy complex configurations. See https://github.com/ohsu-comp-bio/funnel/blob/main/config/config.go or https://github.com/bmeg/grip/blob/develop/config/config.go for examples