Split survey document into multiple documents and collections

[gino-m]

Motivation

• The full set of ACLs should only be visible to survey organizers and owners, not everyone
• When listing available surveys, we only want to fetch the title and description, not the entire survey definition
• Property generator integrations like WHISP want to know which jobs they're enabled for without downloading the entire survey.

Proposed structure

• Documents in /surveys/{surveyId} contain only basic info shown in survey list (title, description, audit info, acls)
• Job definitions move to /surveys/{surveyId}/jobs/{jobId}

Changes required

• Update Android client to read from new structure
• Update web client to read from and write to new structure
• Update import/export Cloud Functions to read from new structure
• Update Cloud Function "survey change" trigger to also trigger on metadata changes
• Update Firestore rules to read from new structure, make ACLs readable only by survey organizers / owners
• Update Storage rules to read from new structure

@rfontanarosa @sufyanAbbasi @scolsen @shobhitagarwal1612 @amysorto Wdyt?

[gino-m]

Being done as part of #1758.