v1.12.0 Release

• Introduced QueryBuilder.CombineUnion(sql string, unionClause string) string to allow specifying how the UNION/UNION ALL statements should be concatenated to the base query.
  To minimize breaking changes the default BaseQueryBuilder implementation is preserved as before - aka. wraps the left and right side of the combined queries in parenthesis (this is not a standard SQL format and it is mostly a MySQL quirk).

• Use custom SqliteQueryBuilder for the SqliteBuilder that removes the default parenthesis wrapping of Union()/UnionAll() statements because otherwise it is causing syntax error (see pocketbase#7516).