Improve UX of Custom Reports for Google Analytics v4

When adding custom reports for GAv4, users have a difficult time validating the field is correct and how to fix the error. Over the last two months, errors with custom reports accounted for 43% of the errors during connector setup.

Example of some errors people see:
> custom_reports is not valid JSON'
> custom_reports is not of type 'array'
> custom_reports: invalid dimension(s)
> custom_reports: invalid metric(s):
> custom_reports.1.pivots.0: 'limit' is a required property
> custom_reports: pages already exist as a default report(s)
> custom_reports.0: 'dimensions' is a required property
> custom_reports.0: 'metrics' is a required property
> custom_reports.0: 'name' is a required property
> custom_reports.0.dimensions.0: {'name': 'city'} is not of type 'string'
> custom_reports.0.dimensions.0: {'name': 'date'} is not of type 'string'
> custom_reports.0.dimensions.0: {'name': 'ga:date'} is not of type 'string'

Observations:
Users have to input custom reports into a single-line field.

Suggestions:
- Instead of having one field to contain multiple custom reports, structure it similar to Google Ads, where each custom report is entered distinctly with it's own name.
- The field that contains the array should be rendered more nicely so that users can validate how it's entered and make any quick adjustments as needed.

It is typically being pasted in from an output generated here: https://ga-dev-tools.google/ga4/query-explorer/. The spec for GAv4 should be updated to accommodate for multiple lines entered in a way that enables the user to make changes without needing scroll back and forth in a small line.

Example of how it's formatted from the query explorer:

How we show it in our app:

Example Fullstory: https://fsty.io/v/DXZWEsMP