[Failure store] Reconciliate failure indices during snapshotting (#118834)

In this PR we reconciliate the failure indices of a data stream just
like we do for the backing indices. The only difference is that a data
stream can have an empty list of failure indices, while it cannot have
an empty list of backing indices.

An easy way to create a situation where certain backing or failure
indices are not included in a snapshot is via using exclusions in the
multi-target expression of the snapshot. For example:

```
PUT /_snapshot/my_repository/my-snapshot?wait_for_completion=true
{
  "indices": "my-ds*", "-.fs-my-ds-000001"
}
```

Author: gmarouli