Log the app config on startup

[smcmurtry]

Summary | Résumé

This commit makes the following changes:

• the config values are now logged when the app starts up, with sensitive values masked
• this is implemented as new class methods on the existing Config class
• new tests added to verify this is working correctly
• add the environs package to force the DEBUG config value to be boolean

This PR shamelessly copies what @patheard did over in this pr to implement the same feature in notification-api.

Related Issues | Cartes liées

https://app.zenhub.com/workspaces/notify-planning-614b3ad91bc2030015ed22f5/issues/gh/cds-snc/notification-planning/504

Test instructions | Instructions pour tester la modification

Test locally to ensure you can see the config values being logged.

Release Instructions | Instructions pour le déploiement

None.

Reviewer checklist | Liste de vérification du réviseur

• This PR does not break existing functionality.
• This PR does not violate GCNotify's privacy policies.
• This PR does not raise new security concerns. Refer to our GC Notify Risk Register document on our Google drive.
• This PR does not significantly alter performance.
• Additional required documentation resulting of these changes is covered (such as the README, setup instructions, a related ADR or the technical documentation).