Make auto generated index name shorter

[zhaih]

See this comment, the auto generated index name could get overlong and JFR is complaining about it. Altho it can be easily overcame by just give the index a dedicated name, but anyway I think make the auto generated index name shorter is still necessary: right now we're trying to list the index spec as part of the name but that will make it extremely hard to open any file using this index name. Perhaps we can just use timestamp as generated index name, and then put the specs in some separated file inside index directory?

[slow-J]

Big +1 to this.

Right now, luceneutil does not work "out of the box" without any local code changes due to the File name too long error that jfr throws.

To reproduce:

1. Set up luceneutil as per the readme.
2. Run python3 src/python/localrun.py -source wikimediumall -r
3. Error gets thrown:

   Create indices:
   /local/home/jslowins/upstream_bench/lucene_bench_home/indices/wikimediumall.lucene_candidate.candidate.facets.taxonomy:Date.taxonomy:Month.taxonomy:DayOfYear.sortedset:Date.sortedset:Month.sortedset:DayOfYear.taxonomy:RandomLabel.sortedset
   :RandomLabel.Lucene90.Lucene99.dvfields.nd33.3326M: now create
   cd /local/home/jslowins/upstream_bench/lucene_bench_home/lucene_candidate/lucene/benchmark
   log /local/home/jslowins/upstream_bench/lucene_bench_home/logs/baseline_vs_patch.wikimediumall.lucene_candidate.candidate.facets.taxonomy:Date.taxonomy:Month.taxonomy:DayOfYear.sortedset:Date.sortedset:Month.sortedset:DayOfYear.taxonomy:
   RandomLabel.sortedset:RandomLabel.Lucene90.Lucene99.dvfields.nd33.3326M.log
   WARNING: Using incubator modules: jdk.incubator.vector
   [0.302s][error][jfr,startup] Could not start recording, not able to write to file /local/home/jslowins/upstream_bench/lucene_bench_home/logs/bench-index-baseline_vs_patch-wikimediumall.lucene_candidate.candidate.facets.taxonomy:Date.taxonomy
   :Month.taxonomy:DayOfYear.sortedset:Date.sortedset:Month.sortedset:DayOfYear.taxonomy:RandomLabel.sortedset:RandomLabel.Lucene90.Lucene99.dvfields.nd33.3326M.jfr. /local/home/jslowins/upstream_bench/lucene_bench_home/logs/bench-index-baselin
   e_vs_patch-wikimediumall.lucene_candidate.candidate.facets.taxonomy:Date.taxonomy:Month.taxonomy:DayOfYear.sortedset:Date.sortedset:Month.sortedset:DayOfYear.taxonomy:RandomLabel.sortedset:RandomLabel.Lucene90.Lucene99.dvfields.nd33.3326M.jf
   r: File name too long
   Error occurred during initialization of VM
   Failure when starting JFR on_create_vm_3