Update timestamp fields to Standard

Timestamp fields we add in service ping are used
to learn how long generation takes and they should
be always be included in payload.

Changelog: changed

config/metrics/license/20210201124932_recorded_at.yml

 ---
-data_category: Optional
+data_category: Standard
 key_path: recorded_at
 description: When the Usage Ping computation was started
 product_section: growth

config/metrics/license/20210204124938_recording_ce_finished_at.yml

 ---
-data_category: Optional
+data_category: Standard
 key_path: recording_ce_finished_at
 description: When the core features were computed
 product_section: growth

doc/development/usage_ping/dictionary.md

@@ -8974,7 +8974,7 @@ When the Usage Ping computation was started
 
 Group: `group::product intelligence`
 
-Data Category: `Optional`
+Data Category: `Standard`
 
 Status: `data_available`
 
@@ -8988,7 +8988,7 @@ When the core features were computed
 
 Group: `group::product intelligence`
 
-Data Category: `Optional`
+Data Category: `Standard`
 
 Status: `data_available`
 
@@ -9002,7 +9002,7 @@ When the EE-specific features were computed
 
 Group: `group::product intelligence`
 
-Data Category: `Subscription`
+Data Category: `Standard`
 
 Status: `data_available`
 

ee/config/metrics/license/20210204124940_recording_ee_finished_at.yml

@@ -9,7 +9,7 @@ value_type: string
 status: data_available
 time_frame: none
 data_source: system
-data_category: Subscription
+data_category: Standard
 distribution:
 - ee
 tier: