SOLR-14251 Add option skipFreeSpaceCheck to split shard operation

[gezapeti]

https://issues.apache.org/jira/browse/SOLR-14251

Description

Adding an option to the SPLIT_SHARD_OP command to make it possible to skip free space checking before splitting shards. This is a workaround as the check logic is broken for shared filesystems.

Solution

The option skips the disk space check as a workaround.

Tests

None.

Checklist

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide

[risdenk]

Fixed a different way in SOLR-16353

[dsmiley]

@risdenk, @gezapeti is already aware; this is complementary. Ideally you could easily globally disable it, but maybe there is a scenario for toggling on a specific request (personally I don't care about the latter; maybe @gezapeti does).

Meanwhile, my colleague @heythm is working on a new Solr utility that would try to make settings like this more regularized so we have it both ways all the time (set via request, or system property, or env variable, or maybe other ways).