add proposal for modify the MaxGasUsedPerBlock

[lyh169]

• 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.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

• Reviewed Files changed in the github PR explorer

---

For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge PR #XYZ: [title]" (coding standards)

[codecov-commenter]

Codecov Report

Merging #209 (a02d44c) into dev (e6ed0b9) will decrease coverage by 0.01%.
The diff coverage is 23.80%.

❗ Current head a02d44c differs from pull request most recent head 22137b0. Consider uploading reports for the commit 22137b0 to get more accurate results

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@@            Coverage Diff             @@
##              dev     #209      +/-   ##
==========================================
- Coverage   34.45%   34.44%   -0.01%     
==========================================
  Files         430      431       +1     
  Lines       44883    44925      +42     
==========================================
+ Hits        15464    15476      +12     
- Misses      28271    28301      +30     
  Partials     1148     1148              

Files Changed	Coverage Δ
app/config/config.go	26.74% <0.00%> (-0.17%)	⬇️
x/params/querier.go	0.00% <0.00%> (ø)
x/params/types/params.go	0.00% <0.00%> (ø)
x/params/types/params_block.go	0.00% <0.00%> (ø)
app/app.go	80.89% <50.00%> (-0.26%)	⬇️
x/params/keeper.go	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes