Ftw.recipe.solr

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- Add configoverlay option. [Kevin Bieri]

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- Add shardsWhitelist to template. [lvonlanthen]

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- Fix detection of running Solr on Linux used in `bin/solr stop` and `bin/solr status`.
[siegy22]

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- Respect SOLR environment variables set outside of the startup script [jone].

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- Update Log4J configuration: Replace log4j.properties with log4j2.xml.
Requires Solr 7.4.0 or later.
[buchi]

- Update default URL and solrconfig.xml to version 8.1.1.
[buchi]

- Add sortable_title and path_depth fields to provided schema.
[buchi]

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- Add ICUNormalizer2CharFilterFactory char filter in provided schema.
This fixes handling of decomposed unicode (aka NFD, NFKD).
[buchi]

- Replace shell process by Solr process when starting in foreground.
[buchi]