Add getLockedStakedAmount

[shuse2]

What was the problem?

This PR resolves #8041

How was it solved?

• Move the getLockedStakedAmount to the internal method and use in endpoint and method
• Expose getLockedStakedAmount from method

How was it tested?

• Add unit test for the getLockedStakedAmount

[codecov]

Codecov Report

Merging #8127 (b9792f1) into development (9893416) will decrease coverage by 0.02%.
The diff coverage is 89.47%.

Additional details and impacted files

@@               Coverage Diff               @@
##           development    #8127      +/-   ##
===============================================
- Coverage        82.87%   82.86%   -0.02%     
===============================================
  Files              579      579              
  Lines            21032    21037       +5     
  Branches          3060     3060              
===============================================
+ Hits             17431    17433       +2     
- Misses            3601     3604       +3     

Impacted Files	Coverage Δ
framework/src/modules/pos/method.ts	90.27% <50.00%> (-2.48%)	⬇️
framework/src/modules/pos/endpoint.ts	97.14% <100.00%> (-0.14%)	⬇️
framework/src/modules/pos/internal_method.ts	100.00% <100.00%> (ø)
framework/src/modules/pos/module.ts	96.60% <100.00%> (ø)
elements/lisk-p2p/src/utils/select.ts	93.75% <0.00%> (-1.25%)	⬇️