Payg Event ingestion should write product tag in Events table

Context:  We currently derive product tag (which is now our identifier) from products/engineering ids later in the process and its messy.  We want to do that determination up front and save it separately to clean up downstream processes.

Done:

• When an event is ingested through service-instance-ingress topic we should determine the product tag using role and product id. Priority will be given to role first since it has to be unique and if its not present then use eng id. Put this is in json and document the schema defn for the other teams to not populate it by themselves.

• We then have to store product tag in Events table in event json for "payg" products. We will add support for non-payg in SWATCH-1993

Note: Adding product tags to new events, and not retroactively assigning them to existing records.  We discussed that blank values shouldn't affect anything because retally doesn't happen anymore.  There will be future cards related to this product name removal work - for hourly/nightly tally - and if we really have to we could add something there that says "if you need the product tag for whatever reason and don't have it, determine it now and save it for later"

Expected end behavior (not sure if QE needs updates to their tests for this):

• Events table has a new column that gets populated with a product tag now.
• This will be visible in the event details as returned by
  • /internal/rpc/tally/events/{org_id}
  • /internal/rpc/tally/events/{event_id}