Track proposal handler events on success

[alexanderbez]

Description

Track any events emitted from a proposal's handler upon successful execution.

closes: #5616

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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
• Re-reviewed Files changed in the Github PR explorer

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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)

[tac0turtle]

[codecov]

Codecov Report

Merging #5622 into master will decrease coverage by 8.9%.
The diff coverage is 27.4%.

@@            Coverage Diff             @@
##           master    #5622      +/-   ##
==========================================
- Coverage   53.43%   44.52%   -8.91%     
==========================================
  Files         322      324       +2     
  Lines       19751    24701    +4950     
==========================================
+ Hits        10553    10998     +445     
- Misses       8381    12643    +4262     
- Partials      817     1060     +243

Impacted Files	Coverage Δ
x/staking/types/types.pb.go	11.02% <ø> (ø)
codec/codec.go	100% <ø> (ø)	⬆️
x/staking/client/cli/query.go	0% <0%> (ø)	⬆️
types/int.go	69.68% <0%> (-0.75%)	⬇️
types/decimal.go	73.07% <0%> (-0.41%)	⬇️
codec/amino.go	45.83% <0%> (ø)	⬆️
types/staking.go	0% <0%> (ø)	⬆️
types/types.pb.go	6.02% <0.81%> (-5.03%)	⬇️
x/staking/keeper/params.go	100% <100%> (ø)	⬆️
x/staking/keeper/query_utils.go	83.87% <100%> (+0.26%)	⬆️
... and 21 more