add application_name_add_host setting

[murex971]

Summary

• Add [general] application_name_add_host (default false, env PGDOG_APPLICATION_NAME_ADD_HOST) to append the client address to application_name as {name} - {ip}:{port}.
• Apply the suffix at login and again when the client changes application_name via SET / set_config, so pg_stat_activity can identify the source of queries.
• If the client sends no application_name, use an empty prefix ( - 10.0.0.5:1234) rather than PgBouncer’s "app" default.

closes #253

[codecov]

Codecov Report

❌ Patch coverage is 99.13043% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/frontend/client/query_engine/query.rs	83.33%	1 Missing ⚠️
pgdog/src/frontend/client/query_engine/set.rs	99.02%	1 Missing ⚠️

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