[Tooling] Add a Flag in the ECS Generator to explicitly exclude one or more fields from the generated artifacts

[djptek]

Summary

Add a Flag in the ECS Generator to explicitly exclude one or more fields from the generated artifacts

Motivation:

Simplify Testing of Deprecation/Removal of Fields, avoiding need to generate a subset of e.g. all but one field

Detailed Design:

Add a flag "--excludeset" e.g.

python scripts/generator.py --ref v1.6.0 \
  --exclude-set       ../my-project/fields/exclude-set.yml \
  --include           ../my-project/fields/custom/ \
  --mapping-settings  ../my-project/fields/mapping-settings.json \
  --out               ../my-project/ \
  --subset            ../my-project/fields/subset.yml \
  --template-settings ../my-project/fields/template-settings.json

• Field names

To be defined ad-hoc

• Example values for the fields

---
- name: log
  fields:
    - name: original

• Suggested appropriate datatypes

n/a

• Any example events that map to the proposed use case(s)

See:
https://github.com/elastic/ecs/blob/master/rfcs/text/0017-remove-log-original.md
https://github.com/elastic/ecs/blob/master/rfcs/text/0022-remove-process-ppid.md

[kgeller]

@djptek is this good to close?

[djptek]

Thanks for the reminder @kgeller this is addressed by merged PR #1411, closing