feat: sign transactions with 2nd mnemonic

[luciorubeens]

Summary

Sign transactions with 2nd mnemonic.

Checklist

• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged

[codecov]

Codecov Report

Merging #2810 into 3.0-react will not change coverage.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##           3.0-react     #2810     +/-   ##
=============================================
  Coverage     100.00%   100.00%             
=============================================
  Files             24       314    +290     
  Lines            142      4042   +3900     
  Branches          18       733    +715     
=============================================
+ Hits             142      4042   +3900     

Flag	Coverage Δ
#unit	100.00% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/app/components/Button/Button.tsx	100.00% <ø> (ø)
src/app/App.tsx	100.00% <100.00%> (ø)
src/app/components/Address/Address.tsx	100.00% <100.00%> (ø)
src/app/components/Alert/Alert.tsx	100.00% <100.00%> (ø)
src/app/components/Amount/Amount.tsx	100.00% <100.00%> (ø)
src/app/components/Avatar/Avatar.tsx	100.00% <100.00%> (ø)
src/app/components/Badge/Badge.tsx	100.00% <100.00%> (ø)
src/app/components/Breadcrumbs/Breadcrumbs.tsx	100.00% <100.00%> (ø)
src/app/components/Card/Card.tsx	100.00% <100.00%> (ø)
src/app/components/Card/CardControl.tsx	100.00% <100.00%> (ø)
... and 334 more

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