fix: invert addWatcher error check and prevent HTTP/TLS server fallthrough in fdbkubernetesmonitor

[Ronitsabhaya75]

addWatcher returned nil on error and retried on success due to err != nil instead of err == nil. This caused file-watch re-establishment to silently fail after ConfigMap remounts, permanently stopping config change detection.

When TLS is configured, the goroutine falls through from the HTTPS block to also start a plain HTTP server on the same port. Added return after the HTTPS block to make the HTTPS-or-HTTP intent explicit.

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