[Visualize] Missing advanced JSON on pipeline aggregations

[markov00]

Kibana version:
master, 7.7

Describe the bug:
When using pipeline aggregation, the Advanced JSON field is only shown on the child aggregation, not on the parent

Steps to reproduce:

1. Create an area chart visualization
2. Add a bucket date histogram agg
3. Change the metric visualization to Serial Diff, the only displayed Advanced field is for the child aggregation, not for the Serial Diff one.

Expected behavior:
The Advanced JSON field should be always available for every aggregation step that can takes extra parameters as it was previously on other older versions like in 7.4

Screenshots (if relevant):

7.7 screenshot (master is the same)

7.4 version (with one advanced field for each aggregation

Errors in browser console (if relevant):
None, but this can create issues when the user tries to add an advanced parameter to the wrong aggregation

Provide logs and/or server output (if relevant):
n/a

Linked issues
A similar issue happen with the custom labels: #69014

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)