Elastic: Fix text search on boolean fields

Elastic: Fix text search on boolean fields

When searching in all fields for a text value, an error was thrown
with ElasticSearch 7.17.23 when the index contains boolean fields:

> query_shard_exception: failed to create query:
> Can't parse boolean value [textvalue], expected [true] or [false]

This patch fixes that problem by skipping boolean fields when the
search word is not the string "true" or "false".