This commit changes the type from "doc" to "_doc" for the
.logstash-management template. Since this is an internally
managed template it does not always go through the REST
layer for it's internal representation. The internal
representation requires the default "_doc" type, which for
external templates is added in the REST layer.
Related #38637
The logstash management template was named in such a way as to confuse
users, who misunderstood it to be a template for indices created by
logstash. It is now renamed to more clearly communicate its purpose and
match the format of the other templates for system indices.