WA-NEW-005: Remove unsupported use_dis_max from query_string queries (ES7)

[kitcommerce]

Extracted from stacked PRs #630/#631 (commit 70fc9db).

In ES7, query_string no longer supports use_dis_max; remove it (and rely on tie_breaker default / existing tie_breaker). Affects admin index search, help search, product search.

Target: next.

[kitcommerce]

Build Gate Failed

rubocop

Rakefile:80:11 Layout/SpaceAroundOperators Operator `<<` should be surrounded by a single space.
core/lib/workarea/configuration.rb:955:7 Layout/CommentIndentation Incorrect indentation detected (column 6 instead of 0).
core/lib/workarea/ext/freedom_patches/bson_document.rb:10:1 Layout/TrailingWhitespace Trailing whitespace detected.
core/test/lib/workarea/elasticsearch/document_test.rb:114:1 Layout/TrailingWhitespace Trailing whitespace detected.

Branch: wa-new-005-remove-use-dis-max
PR: #649

Once fixed + pushed, re-apply status:ready-for-review and the dispatcher will re-run build gate + review waves.