[Hotfix] prevent huge gas tx

[yun-yeo]

Summary of changes

• The ante handler will block the tx with high gas than 30,000,000
• Update ConsensusParams MaxGas = 30,000,000

Expected Update Time

// Expected time:
// MAINNET
// Tue Mar 30 2021 18:00:00 GMT+0900 (KST)
// Tue Mar 30 2021 09:00:00 GMT+0000 (UTC)
// Tue Mar 30 2021 01:00:00 GMT-0800 (PST)
//
// TEQUILA
// Tue Mar 25 2021 18:00:00 GMT+0900 (KST)
// Tue Mar 25 2021 09:00:00 GMT+0000 (UTC)
// Tue Mar 25 2021 01:00:00 GMT-0800 (PST)

Report of required housekeeping

• Github issue OR spec proposal link
• Wrote tests
• Updated API documentation (client/lcd/swagger-ui/swagger.yaml)
• Added a relevant changelog entry: clog add [section] [stanza] [message]

---

(FOR ADMIN) Before merging

• Added appropriate labels to PR
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)
• Confirm added tests are consistent with the intended behavior of changes
• Ensure all tests pass

[codecov]

Codecov Report

Merging #462 (ac15ae5) into master (4478905) will increase coverage by 0.15%.
The diff coverage is 75.00%.

❗ Current head ac15ae5 differs from pull request most recent head c1651bc. Consider uploading reports for the commit c1651bc to get more accurate results

@@            Coverage Diff             @@
##           master     #462      +/-   ##
==========================================
+ Coverage   67.21%   67.36%   +0.15%     
==========================================
  Files         119      119              
  Lines        5124     5127       +3     
==========================================
+ Hits         3444     3454      +10     
+ Misses       1460     1452       -8     
- Partials      220      221       +1     

Impacted Files	Coverage Δ
x/auth/ante/spamming_prevention.go	84.61% <75.00%> (+74.61%)	⬆️