feat: make query parser optional for load balancing

[levkk]

fix #690

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/frontend/router/parser/query/mod.rs	41.66%	7 Missing ⚠️
pgdog/src/backend/pool/cluster.rs	85.71%	2 Missing ⚠️

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