[7.x][docs] Backport: Add abbreviated titles for a cleaner nav (#16537)

[dedemorton]

Backports #16537 to 7.x branch.

[chipzzz]

@dedemorton , for add_fields

with the following config:

processors:
- add_fields:
    fields:
      test.newfield: dupa

you get fields.test.newfield as the field name. This is confusing as fields is part of the field name, where from the docs it looks like it's supposed to be used as a parameter.

This was noticed un functionbeat 7.x config

[chipzzz]

@dedemorton , actually it's because of this

target (Optional) Sub-dictionary to put all fields into. Defaults to fields. I guess I must add target if I want my own top level field

[dedemorton]

Yes, that's right. It looks like the published docs are correct. If you have additional feedback, please open a new GitHub issue rather than commenting on merged pull requests.

If you have questions, please post them to the discuss forum: https://discuss.elastic.co/c/beats. Thanks!