Besides a rename, this changes allows to processor to attach multiple
enrich docs to the document being ingested.
Also in order to control the maximum number of enrich docs to be
included in the document being ingested, the `max_matches` setting
is added to the enrich processor.
Relates #32789
Enrich processor configuration changes:
* Renamed `enrich_key` option to `field` option.
* Replaced `set_from` and `targets` options with `target_field`.
The `target_field` option behaves different to how `set_from` and
`targets` worked. The `target_field` is the field that will contain
the looked up document.
Relates to #32789
If a pipeline that refrences the policy exists, we should not allow the
policy to be deleted. The user will need to remove the processor from
the pipeline before deleting the policy. This commit adds a check to
ensure that the policy cannot be deleted if it is referenced by any
pipeline in the system.