feat: rds iam passthrough auth

[levkk]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 52.97030% with 95 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/auth/token_cache.rs	0.00%	56 Missing ⚠️
pgdog/src/frontend/client/mod.rs	35.71%	9 Missing ⚠️
pgdog/src/backend/pool/connection_creation.rs	89.33%	8 Missing ⚠️
pgdog/src/backend/pool/pool_impl.rs	27.27%	8 Missing ⚠️
pgdog/src/backend/pool/address.rs	0.00%	7 Missing ⚠️
pgdog/src/backend/disconnect_reason.rs	57.14%	3 Missing ⚠️
pgdog/src/backend/pool/password.rs	0.00%	3 Missing ⚠️
pgdog-config/src/auth.rs	75.00%	1 Missing ⚠️

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