…jects (elastic#175970)

When there are multiple dynamic templates with the same name, we only
use the first appearance.
Add an exception for intermediate objects, so we use the last
appearance. This way we avoid that less specific dynamic templates
created for intermediate objects match before more specific dynamic
templates defined in packages.

This was a problem for example in the Prometheus package, where there
are definitions for `prometheus.*.value` and `prometheus.*.histogram`.
For both cases Fleet tries to create a dynamic template for the
intermediate objects `prometheus.*`. If this dynamic template is
inserted before the dynamic template for the histograms, it matches for
them, causing mapping errors on ingestion, like the following one:
```
mapper [prometheus.queue_duration.histogram.values] cannot be changed from type [float] to [long]
```
With this change, when multiple definitions generate the same dynamic
template for intermediate objects, only the last one ends up in the
template.

These intermediate objects were introduced in 8.12, after elastic#169981.

(cherry picked from commit 7274f6e)