Solr >=7 errors on field_session_min_age/max_age

[froboy]

As per this issue on drupal.org, field_session_min_age and field_session_max_age will throw errors with Solr >=7 and Search_api_solr 4.2.7. This isn't happening on the sandbox because it's still using Solr 4.

Observed behavior:

• spin up an environment with solr 7 or 8
• drush en openy_prgf_af4_demo
• see this error on /activity-finder-v4

Drupal\search_api_solr\SearchApiSolrException: Facets having a mincount of "0" is not yet supported by Solr for point based field types. Consider converting the following field to a string or index it twice as string: field_session_min_age. in Drupal\search_api_solr\Plugin\search_api\backend\SearchApiSolrBackend->setFacets() (line 3552 of modules/contrib/search_api_solr/src/Plugin/search_api/backend/SearchApiSolrBackend.php).

Expected behavior:
No error and age facets behave as expected.

[shelleygoetz]

@froboy Jira ticket created: https://openy.atlassian.net/browse/MAINTAIN-266