chore(epic-idpe-17711): use SQL HTTP API to get field list

[appletreeisyellow]

Wait for #6783 to merge

Part of https://github.com/influxdata/idpe/issues/17981

This PR uses the SQL HTTP API to query fields

The change is behind the feature flag v2privateQueryUI and it is set to false by default

To test locally

1. Deploy the remocal with the following flag:

   make deploy-remocal DEPLOY_IOX=true ENABLE_IOX_FLIGHT=true
   

2. Then you will see the query for measurement list will send to /api/v2private/query in DevTool Network tab

Before and After

Screen.Recording.2023-08-22.at.4.16.40.PM.mov

Checklist

Authors and Reviewer(s), please verify the following:

• A PR description, regardless of the triviality of this change, that communicates the value of this PR
• Well-formatted conventional commit messages that provide context into the change
• Documentation updated or issue created (provide link to issue/PR)
• Signed CLA (if not already signed)
• Feature flagged, if applicable

[wdoconnell]

Looks good. One minor non-blocking comment re: one type cast.

[wdoconnell]

Is the reason we don't get strong typing here (and have to type cast using as) that we can't predict the type of resp.parsed.table.columns.column_name.data?

[appletreeisyellow]

@wdoconnell We actually can predict the type of resp.parsed.table.columns.column_name.data which is string[] | number[] | boolean[]. Since field keys are strings, so we cast the data to string[] specifically