refactor: revisit foundation operator

[0Tech]

Description

This patch will replace the foundation operator into the module's authority. As of now, the authority MUST be the module account of x/foundation.
Someday, we may change the authority to x/gov's. This patch would open the possibility.

closes: #741

Checklist:

• I followed the contributing guidelines and code of conduct.
• I have added a relevant changelog to CHANGELOG.md
• I have added tests to cover my changes.
• I have updated the documentation accordingly.
• I have updated API documentation client/docs/swagger-ui/swagger.yaml

[codecov]

Codecov Report

Merging #744 (989bc3a) into main (da194c7) will decrease coverage by 0.05%.
The diff coverage is 98.52%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #744      +/-   ##
==========================================
- Coverage   62.08%   62.03%   -0.06%     
==========================================
  Files         877      877              
  Lines       98970    98948      -22     
==========================================
- Hits        61450    61382      -68     
- Misses      33900    33955      +55     
+ Partials     3620     3611       -9     

Impacted Files	Coverage Δ
x/foundation/keeper/exec.go	93.05% <85.71%> (+0.19%)	⬆️
simapp/app.go	86.11% <100.00%> (ø)
x/foundation/client/testutil/suite.go	97.68% <100.00%> (-0.17%)	⬇️
x/foundation/client/testutil/tx.go	100.00% <100.00%> (ø)
x/foundation/genesis.go	83.21% <100.00%> (-0.46%)	⬇️
x/foundation/keeper/genesis.go	96.77% <100.00%> (-0.41%)	⬇️
x/foundation/keeper/keeper.go	89.47% <100.00%> (+6.14%)	⬆️
x/foundation/keeper/member.go	95.00% <100.00%> (-0.21%)	⬇️
x/foundation/keeper/msg_server.go	84.91% <100.00%> (ø)
x/foundation/keeper/proposal.go	88.69% <100.00%> (ø)
... and 4 more

[tkxkd0159]

LGTM