op-challenger: Allow specifying a chain ID as network.

[ajsutton]

op-program supports custom configs identified by chain ID so make sure op-challenger can pass through a chain ID option even if it isn't a known network.

[Inphi]

I'm not a fan of type-punning chain-ids into --network. It's too late to change now though given that the op-program does it this way.

[ajsutton]

We could change op-program as well if we wanted to - this clearly isn't getting much use if it doesn't work in op-challenger yet. I tend to favour this solution as otherwise we need to add a lot more boilerplate code and complexity in deciding what to pass through to challenger etc. I'm open to other ideas though.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.73%. Comparing base (980b261) to head (3e5b282).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #13027      +/-   ##
===========================================
- Coverage    44.42%   42.73%   -1.70%     
===========================================
  Files          798      742      -56     
  Lines        71680    67017    -4663     
===========================================
- Hits         31846    28639    -3207     
+ Misses       37246    35972    -1274     
+ Partials      2588     2406     -182     

Flag	Coverage Δ
cannon-go-tests-32	?
cannon-go-tests-64	?

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Files with missing lines	Coverage Δ
op-challenger/config/config.go	95.21% <100.00%> (+0.05%)	⬆️

... and 62 files with indirect coverage changes