Add max tx gas limit

[philipsu522]

Describe your changes and provide context

Add a config for max tx gas, and drop transactions on propose

Testing performed to validate your change

[codecov]

Codecov Report

Attention: Patch coverage is 56.52174% with 10 lines in your changes missing coverage. Please review.

Project coverage is 58.18%. Comparing base (57e0107) to head (3959557).

Files with missing lines	Patch %	Lines
internal/mempool/metrics.gen.go	66.66%	6 Missing ⚠️
internal/mempool/mempool.go	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #251      +/-   ##
==========================================
+ Coverage   58.10%   58.18%   +0.08%     
==========================================
  Files         249      249              
  Lines       34555    34567      +12     
==========================================
+ Hits        20079    20114      +35     
+ Misses      12877    12854      -23     
  Partials     1599     1599              

Files with missing lines	Coverage Δ
config/config.go	63.18% <100.00%> (+0.06%)	⬆️
internal/mempool/mempool.go	72.97% <0.00%> (-0.45%)	⬇️
internal/mempool/metrics.gen.go	15.95% <66.66%> (-0.14%)	⬇️

... and 18 files with indirect coverage changes