feat: make query parser optional for load balancing

[levkk]

fix #690

[codecov]

Codecov Report

❌ Patch coverage is 92.26190% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog-config/src/core.rs	59.09%	9 Missing ⚠️
pgdog/src/admin/set.rs	0.00%	2 Missing ⚠️
pgdog/src/backend/pool/cluster.rs	94.11%	1 Missing ⚠️
pgdog/src/frontend/router/parser/query/mod.rs	96.15%	1 Missing ⚠️

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