We change strategy to select indexes for reindexing:

1. Consider relative bloat levels instead of absolute bloat
1. Exclude GIN indexes (risk for GitLab.com)
1. Exclude indexes with relative bloat level < 20%
1. Exclude indexes < 1 GB ondisk size (not worth it for now)
1. Exclude indexes > 100 GB ondisk size (risk for GitLab.com)
1. Don't reindex an index twice within 10 days

Together with adding support for unique indexex in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64695, this
aims to distribute reindexing actions better across indexes and exclude
the risky ones.

Relates to:

- https://gitlab.com/gitlab-org/gitlab/-/issues/335295
- https://gitlab.com/gitlab-org/gitlab/-/issues/335214
- https://gitlab.com/gitlab-org/gitlab/-/issues/335211

Related discussion in :

-
https://gitlab.com/gitlab-com/gl-infra/production/-/issues/5069#note_618889225