feat: liquidator query enabled by runtime flag

[toteki]

Description

The query liquidation-targets is enabled at runtime the node is started with a flag:

# Enabled
umeed start --enable-liquidator-query

# Enabled
umeed start -l

# Disabled
umeed start

closes: #1400

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[robert-zaremba]

Let's avoid the global variables, especially if we modify them in tests, and even more especially if they are pointers.

[codecov-commenter]

Codecov Report

Merging #1577 (c1115dd) into main (56b89e0) will increase coverage by 0.10%.
The diff coverage is 68.57%.

@@            Coverage Diff             @@
##             main    #1577      +/-   ##
==========================================
+ Coverage   52.08%   52.18%   +0.10%     
==========================================
  Files          72       73       +1     
  Lines        7092     7105      +13     
==========================================
+ Hits         3694     3708      +14     
+ Misses       3125     3124       -1     
  Partials      273      273              

Impacted Files	Coverage Δ
x/leverage/module.go	56.92% <0.00%> (-1.81%)	⬇️
x/oracle/types/keys.go	45.71% <0.00%> (+3.60%)	⬆️
util/bytes.go	100.00% <100.00%> (ø)
x/leverage/keeper/grpc_query.go	64.17% <100.00%> (ø)
x/oracle/keeper/historic_price.go	93.93% <100.00%> (+0.12%)	⬆️

[robert-zaremba]

thanks. LGTM.