fix(test-db): engine params

[betodealmeida]

SUMMARY

Improve the test-db command so that we can pass more than just connect_args when creating an engine; this is needed for BigQuery, eg, where the create_engine looks like this:

engine = create_engine("bigquery://", credentials_info=...)

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TESTING INSTRUCTIONS

Run:

flask preset test-db 'bigquery://' -c '{"credentials_info": ...}'

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[betodealmeida]

This is the main change in the PR, everything else is just renaming the variable.