Update links to Learn section of metabase.com (#46336)

docs/databases/users-roles-privileges.md

docs/exploration-and-organization/collections.md

docs/people-and-groups/google-and-ldap.md

docs/permissions/data-sandboxes.md

docs/permissions/introduction.md

docs/questions/native-editor/sql-parameters.md

docs/questions/query-builder/expressions/case.md

docs/questions/query-builder/expressions/coalesce.md

docs/questions/query-builder/expressions/concat.md

docs/questions/query-builder/expressions/converttimezone.md

docs/questions/query-builder/expressions/countif.md

docs/questions/query-builder/expressions/datetimeadd.md

docs/questions/query-builder/expressions/datetimediff.md

docs/questions/query-builder/expressions/datetimesubtract.md

docs/questions/query-builder/expressions/isempty.md

docs/questions/query-builder/expressions/isnull.md

docs/questions/query-builder/expressions/now.md

docs/questions/query-builder/expressions/offset.md

docs/questions/query-builder/expressions/regexextract.md

docs/questions/query-builder/expressions/substring.md