ZRFE-909: By default, gather all gc.log files since they're split into 10MB chunks

[jholder85638]

When zmdiaglog is run, it only gathers gc.log
Starting in 8.5, we split gc.log into 10MB chunks. This can cause an issue for support as if GC issues are happening, we cannot see them in gc.log.x
This commit gathers all gc.log.x files.

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