Change/fix [DeadLetterQueueReader] java.nio.file.NoSuchFileException logs

[edmocosta]

The DeadLetterQueueReader is noisily generating java.nio.file.NoSuchFileException WARN logs when it tries to execute the age police and invokes compareByFileTimestamp with already deleted segments. It happens more often when dead_letter_queue.storage_policy is set to drop_older raising this exception.

It seems to be expected as the file was dropped by the writer. But this logger is noisy, and we should reconsider if it really needs to be a WARN as there's no action users can take to remediate it.

Raise this exception is also avoidable and fixing it would be an option.

[2023-08-25T00:00:24,648][WARN ][org.logstash.common.io.DeadLetterQueueReader][test][4196a11abbf21202155069807a4472eb6e89a5dfb2989cea89d38f66a3656de1] Error reading file's timestamp for /var/lib/logstash/test/test/41.log
java.nio.file.NoSuchFileException: /var/lib/logstash/test/test/41.log
	at sun.nio.fs.UnixException.translateToIOException(UnixException.java:92) ~[?:?]
	at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:106) ~[?:?]
	at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:111) ~[?:?]
	at sun.nio.fs.UnixFileAttributeViews$Basic.readAttributes(UnixFileAttributeViews.java:55) ~[?:?]
	at sun.nio.fs.UnixFileSystemProvider.readAttributes(UnixFileSystemProvider.java:148) ~[?:?]
	at sun.nio.fs.LinuxFileSystemProvider.readAttributes(LinuxFileSystemProvider.java:99) ~[?:?]
	at java.nio.file.Files.readAttributes(Files.java:1851) ~[?:?]
	at java.nio.file.Files.getLastModifiedTime(Files.java:2402) ~[?:?]
	at org.logstash.common.io.DeadLetterQueueReader.compareByFileTimestamp(DeadLetterQueueReader.java:389) ~[logstash-core.jar:?]