feat(ante)!: Ante handler to add a maximum commission rate of 25% for validators.

[Unique-Divine]

Purpose

In our validator interviews, we found that a common strategy for "low-commission attacking" validators is to:

1. Set a normal commission rate
2. Then, change the commission rate to be extremely low to undercut the other validators and advertise for delegations
3. And finally, adjust the commission extremely high to rake in profits with the new delegations.

If you impose a reasonable minimum and maximum commission, this problem is almost entirely avoided.

• Related to feat(ante): set minimum commission percentage for validating #1588

[codecov]

Codecov Report

Merging #1615 (ced79b2) into master (f1e92a5) will increase coverage by 0.07%.
Report is 1 commits behind head on master.
The diff coverage is 100.00%.

❗ Current head ced79b2 differs from pull request most recent head 3e6873d. Consider uploading reports for the commit 3e6873d to get more accurate results

@@            Coverage Diff             @@
##           master    #1615      +/-   ##
==========================================
+ Coverage   74.18%   74.25%   +0.07%     
==========================================
  Files         165      167       +2     
  Lines       13177    13201      +24     
==========================================
+ Hits         9775     9803      +28     
+ Misses       2855     2850       -5     
- Partials      547      548       +1     

Files	Coverage Δ
app/ante.go	54.00% <100.00%> (+0.93%)	⬆️
app/ante/commission.go	100.00% <100.00%> (ø)
app/ante/errors.go	100.00% <100.00%> (ø)
app/ante/fixed_gas.go	100.00% <100.00%> (ø)
x/common/testutil/cli/network.go	74.05% <100.00%> (ø)

... and 1 file with indirect coverage changes

[Unique-Divine]

Somehow, gas decreases due to this change. I have no idea why