Drop liquidity orders from matched orders metric

[MartinquaXD]

Fixes #129

The "Matched Orders" panel in Grafana currently includes liquidity orders. If there are many liquidity orders the graph for matched orders declines significantly making it seem like our service is experiencing issues.
This can be solved by introducing a metric which only tracks how many user orders have been created. If we use this metric in the Grafana panel the "Matched Orders" graph will better reflect the user experience of the service.

Test Plan

Local test submitting 1 user order and 1 liquidity order.
New metric counting user orders:

# HELP gp_v2_api_orderbook_user_orders_created Number of user (non-liquidity) orders created.
# TYPE gp_v2_api_orderbook_user_orders_created counter
gp_v2_api_orderbook_user_orders_created 1

Metric we previously in the Grafana panel

# HELP gp_v2_api_api_requests_complete Number of completed API requests.
# TYPE gp_v2_api_api_requests_complete counter
gp_v2_api_api_requests_complete{method="v1/create_order",status_code="201"} 2

This shows that the new metrics is working and ignores liquidity orders.

[nlordell]

LGTM.

As a side note I think that we should add the is_liquidity_order flag to the OrderMetadata as well - this is so we don't need to ensure that the API and service are configured with the same liquidity owners.

[codecov-commenter]

Codecov Report

Merging #167 (9913fe3) into main (1416209) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #167      +/-   ##
==========================================
- Coverage   64.83%   64.82%   -0.01%     
==========================================
  Files         185      185              
  Lines       38388    38398      +10     
==========================================
+ Hits        24889    24893       +4     
- Misses      13499    13505       +6     

[nlordell]

@MartinquaXD Does this also fix our time to trade metric?

[MartinquaXD]

Does this also fix our time to trade metric?

No, it doesn't. But looking at the code the fix should be trivial. I'll submit a PR.