chore: update check transaction task

[pawellewandowski98]

Description

• Changed number of transactions which are checked in task
• Updated db query conditions because MongoDB do not have default values like PostgreSQL (example block_height = 0) we need to get also headers with block_height = nil

[codecov]

Codecov Report

Merging #352 (9bbd8f4) into master (b7213a1) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #352      +/-   ##
==========================================
- Coverage   52.13%   52.11%   -0.02%     
==========================================
  Files          90       90              
  Lines       10677    10681       +4     
==========================================
  Hits         5566     5566              
- Misses       4686     4690       +4     
  Partials      425      425              

Flag	Coverage Δ
unittests	52.11% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
model_transactions.go	61.77% <0.00%> (-0.37%)	⬇️
tasks.go	0.00% <0.00%> (ø)

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[mrz1836]

LGTM