Fix DSN parsing when creating connection (#90)

- Use regex to validate DSN and extract parts
- Add `ConfigUtils.ResolvedField<T>` which represents a connection property which may have an associated error
- Add `EdgeDBConnection._FromResolvedFields`
    - Performs final validation
    - Raises any errors from properties if present
    - Constructs a valid connection object
- Moves `ParseWaitUntilAvailable` to `ConfigUtils`