src: allow empty --experimental-config-file

[marco-ippolito]

This PR makes --experimental-config-file accept no arg.
When no arg is passed, it will default to node.config.json.
--experimental-default-config-file is just an alias of --experimental-config-file.
The reason for this change is so when stable we can just remove --experimental-default-config-file and rename --experimental-config-file to --config-file.
Users can execute node with node --config-file index.js or node --config-file=foo.json index.js.

[nodejs-github-bot]

Review requested:

• @nodejs/config

[pmarchini]

LGTM

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/71151/

[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.74%. Comparing base (f6464c5) to head (9b00ced).

Files with missing lines	Patch %	Lines
src/node_config_file.cc	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61610      +/-   ##
==========================================
- Coverage   89.76%   89.74%   -0.03%     
==========================================
  Files         673      673              
  Lines      203944   203954      +10     
  Branches    39191    39192       +1     
==========================================
- Hits       183080   183046      -34     
- Misses      13194    13234      +40     
- Partials     7670     7674       +4     

Files with missing lines	Coverage Δ
lib/internal/process/pre_execution.js	95.84% <100.00%> (-0.13%)	⬇️
src/node_options.cc	76.32% <100.00%> (+0.04%)	⬆️
src/node_config_file.cc	82.54% <87.50%> (+0.59%)	⬆️

... and 31 files with indirect coverage changes

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