[reginaldalfret]

Description of changes

This change ensures that a custom logger supplied via the programmatic WithLogger option is preserved when CLI flags or configuration files specify --structured-logs or --quiet.

1. Preserve custom logger:

   • Previously in loadConfig, c.logger was unconditionally re-assigned if c.conf.StructuredLogs or c.conf.Quiet was true, overwriting any custom cloudsql.Logger passed by the caller in WithLogger.
   • Added a customLogger indicator to Command set by WithLogger so that custom loggers take precedence over default logger instantiation.

2. Add WithStructuredLogging() Option:

   • Added WithStructuredLogging() to cmd/options.go alongside WithQuietLogging() and WithDebugLogging(), allowing programmatic enablement of structured JSON logging.

3. Regression Tests:

   • Added WithStructuredLogging test case to TestCommandOptions.
   • Added TestCommandOptionsOverridesCLI test cases verifying that WithLogger takes precedence when --structured-logs or --quiet flags are supplied.

[blacksoxx]

Ran this locally at d8a38c5: it merges clean with current main, go test -race ./cmd -run TestCommandOptions passes, and with only the two new WithLogger cases applied on main both fail with "custom logger was overridden", so the tests pin the behaviour change. go vet is clean.

The customLogger flag reads fine to me and keeps --quiet and --structured-logs working for callers who do not pass a logger. Nothing else from my side; the failing E2E check is the usual secrets gate for outside PRs rather than anything in this diff.