Add explicitly lenient option

[lasseborly]

This is a fairly commonly used options that would be nice to surface a bit.

https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-simple-query-string-query.html

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[coveralls]

Coverage remained the same at 98.69% when pulling d2aa53c on lasseborly:patch-1 into fefd99a on searchkit:develop.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.