Non-existing location for default gc.log file

[ankon]

bin/elasticsearch.in.sh specifies that the GC log file should be stored at /var/log/elasticsearch/gc.log (when ES_USE_GC_LOGGING is set).

This location would not exist by default, and I also think it is a rather odd place given that other logs end up in the (existing) logs directory.

Could this be changed to

1. by default use $ES_HOME/logs/gc.log
2. be overrideable by another setting so one doesn't need to modify the script file

This issue has now caused about 50% of my node restarts when updating ... I always forget about it, see the error, wait for the cluster to be reasonable, and then restart again :)

[ankon]

PR #8479 has a fix for this issue.

Note that the windows .bat file already did the right thing, so the PR makes windows and !windows behave in the same way, and then adds the ability to configure the name of the log file from the outside.