Update statistics when reindexing a functional index

The reindexing feature creates a new index, swaps it with the original one and drops the original index afterwards.

This has led to gitlab-com/gl-infra/production#2885 (closed), which was caused by missing statistics for a functional index.

For functional indexes, the reindexing feature needs to update statistics through ANALYZE $table after creating the new index.

We might also want to add an assertion to check that statistics are present before dropping the old index:

select count(*) from pg_statistic where starelid = (select oid from pg_class where relname = 'index_name');