Admin: add total index memory in `_cat/indices`

This patch adds to `_cat/indices` information about memory usage per index by adding memory used by FieldData, IdCache, Percolate, Segments (memory, index writer, version map).

```
% curl 'localhost:9200/_cat/indices?v&h=i,tm'
i     tm
wiki  8.1gb
test  30.5kb
user  1.9mb
```

Closes #7008
Docs: clarify wait_for_completion flag in snapshot documentation

Closes #7952
Tests: two corruptions can fix a file

In some of our tests we corrupt multiple places in a file randomly. If we corrupt the same place twice, we shouldn't fix the file by mistake.
Docs: Added breaking changes docs for Indices APIs

Adds the breaking changes defaults for the change of default indices options for the GET Aliases API
Parent/child: has_parent filter must take parent filter into account when executing the inner query/filter.

Closes #8020
Closes #7943