Add ability to set database connection string

[pbolduc]

Description

Adds the ability to use an optional onnectionString property. This would allow customizing any of the connecting string properties without having to configure each property individually.

Fixes #220

Types of changes

Checklist

• [x] I have read the CONTRIBUTING doc
• [ ] I have checked that unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)

Further comments

[pbolduc]

I understand your team is currently in the process of a major 0.7 release. I would appreciate once the dust settles, if you could discuss and review this PR. I understand there may not be an appetite for exposing the connection string as a configuration variable directly.

[pbolduc]

For reference, I believe the Postgres client uses node-postgres which in turn uses pg-connection-string for parsing connection strings. The pg-connection-string package provides docs on the options for this field.

[TimCsaky]

Closing this because it's been a few months. We have captured this task in our backlog as a feature we may want to implement at a later date.