[Change Proposal] Resolve use of unspecified fields in the integrations packages field description files

During work on an ECS and pipeline description analysis tool I found that a variety of fields used in integration package field descriptions are not specified. After discussion with @andrewkroh on what to do with these we decided to file this catch-all issue for either letting teams remove the fields and/or for people to have a discussion here to resolve the specification of the fields.

The list is long so it is available at [this gist](https://gist.github.com/efd6/7e91232f4f6ff971106e501cf0aef16a#file-fields-md).

The code used to generate the list is [here](https://gist.github.com/efd6/7e91232f4f6ff971106e501cf0aef16a#file-main-go). The output can be regenerated for any commit by checking out the commit and running the code in the packages directory of the [github.com/elastic/integrations](https://github.com/elastic/integrations/) repo.