Fields are only refreshed from the last five indexes

[zhaakhi]

In settings > indices, when you press "reload field list" for a time-based index pattern, fields are only fetched from the last five indices.

Fields that are not present in those will not show up in the field list, and will show a 'no cached mapping for this field' warning when they show up in Discover.

This was a point of confusion for me because

1. It is not obvious that only five indices will be checked
2. There is no clear way to override this behaviour

I recommend to make it clearer which indices are read, and to have a way to force the refresh to read all matching indices.

[jimmyjones2]

See #2928

[rashidkpc]

As noted, duplicate of #2928