SOLR-17330: When not set, loadOnStartup defaults to true

[psalagnac]

SOLR-17330

Description

That's a pretty small change, replacing default value for loadOnStartup from false to true when the value is missing from core properties.
The default value when creating a new core is already true, so I don't expect any behavior change. Fixing this because I wasted some time understanding the code because of the inconsistent values.

I filled a Jira to track it, but I did not update the CHANGES file since no user should perceive the change (let me know if that's necessary).

Solution

Just set default to true.

Tests

None

Checklist

Please review the following and check all that apply:

• 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

[epugh]

Lgtm. Maybe a diggers variable name than tmp or even just inline it since we do that often? Love the cleanup

[epugh]

Will merge tomorrow, assigned it to me so I do not forget!!