Parametrise simulation gas value

[alessio]

Reported by @migueldingli1997

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[fedekunze]

utACK

[alexanderbez]

utACK

[codecov]

Codecov Report

Merging #5419 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #5419      +/-   ##
==========================================
- Coverage    54.6%   54.59%   -0.01%     
==========================================
  Files         315      315              
  Lines       18919    18921       +2     
==========================================
  Hits        10330    10330              
- Misses       7808     7810       +2     
  Partials      781      781

Impacted Files	Coverage Δ
simapp/test_helpers.go	0% <0%> (ø)	⬆️