Set unique values for docsearch version_rank

[rwinch]

Right now the latest version is ranked highest, but we could improve this so that other versions are ranked properly too. See

spring-security/.github/actions/docsearch-config.json.hbs

Line 10 in ac8e3f6

"version_rank": {{#if (eq ./activeVersionSegment '')}}1{{else}}2{{/if}}