Follow up for #23405.
We remove azure deprecated settings in 7.0:
* The legacy azure settings which where starting with `cloud.azure.storage.` prefix have been removed.
This includes `account`, `key`, `default` and `timeout`.
You need to use settings which are starting with `azure.client.` prefix instead.
* Global timeout setting `cloud.azure.storage.timeout` has been removed.
You must set it per azure client instead. Like `azure.client.default.timeout: 10s` for example.
* Remove the _all metadata field
This change removes the `_all` metadata field. This field is deprecated in 6
and cannot be activated for indices created in 6 so it can be safely removed in
the next major version (e.g. 7).
We use `:` for cross-cluster search (eg `cluster:index`), therefore, we should
not allow the ambiguity when allowing cluster or index names.
Relates to #23892
