Sync schema with ETL query (mozilla#421)

Update the search_clients_daily schema to match the ETL query:

* submission_date_s3 - Not in ETL query, but does appear to be
  available in recent queries
* tagged-sap - tagged_sap (underscore) in ETL query
* tagged-follow-on - tagged_follow_on (underscores) in ETL query
* normalized_engine - In ETL query, not in schema
* user_pref_browser_search_region - In ETL query, not in schema
* is_default_browser - In ETL query, not in schema
* experiments -  In ETL query, not in schema

The schema appears to be a generated section, but these changes are
hand-edited.  The types are my best guess from looking at the code.

Author: jwhitlock

src/datasets/search/search_clients_daily/reference.md

@@ -60,15 +60,21 @@ root
  |-- tab_open_event_count_sum: long (nullable = true)
  |-- active_hours_sum: double (nullable = true)
  |-- total_uri_count: long (nullable = true)
- |-- tagged-sap: long (nullable = true)
- |-- tagged-follow-on: long (nullable = true)
+ |-- tagged_sap: long (nullable = true)
+ |-- tagged_follow_on: long (nullable = true)
  |-- sap: long (nullable = true)
  |-- tagged_sap: long (nullable = true)
  |-- tagged_follow_on: long (nullable = true)
  |-- organic: long (nullable = true)
  |-- search_with_ads: long (nullable = true)
  |-- ad_click: long (nullable = true)
  |-- unknown: long (nullable = true)
+ |-- normalized_engine: string (nullable = true)
+ |-- user_pref_browser_search_region: string (nullable = true)
+ |-- is_default_browser: boolean (nullable = true)
+ |-- experiments: map (nullable = true)
+ |    |-- key: string
+ |    |-- value: string
 ```
 
 # Code Reference