test: Allow to add new validator in test network

[kukugi]

Description

Add new function to add a validator to test network. multi node cli test use this function when running test case of adding and promoting new node.

it placeed lbm-sdk side because it need to run without lock

closes: #XXXX

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• 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
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #193 (340dcbf) into v2/develop (0ee1980) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

❗ Current head 340dcbf differs from pull request most recent head a85cf6f. Consider uploading reports for the commit a85cf6f to get more accurate results

@@              Coverage Diff               @@
##           v2/develop     #193      +/-   ##
==============================================
- Coverage       53.10%   53.09%   -0.01%     
==============================================
  Files             688      688              
  Lines           49052    49057       +5     
==============================================
  Hits            26048    26048              
- Misses          20110    20115       +5     
  Partials         2894     2894              

Impacted Files	Coverage Δ
testutil/network/network.go	84.45% <0.00%> (-1.82%)	⬇️
x/wasm/internal/keeper/keeper.go	86.14% <0.00%> (-0.38%)	⬇️
snapshots/store.go	75.40% <0.00%> (+1.09%)	⬆️