feat(jellyfish-api-core): add blockchain getMempoolDescendants RPC

[helloscoopa]

What this PR does / why we need it:
/kind feature

Which issue(s) does this PR fixes?:
Fixes part of #48

• Implements getmempooldescendants type for RPC.

[codeclimate]

Code Climate has analyzed commit 886b8dc and detected 1 issue on this pull request.

Here's the issue category breakdown:

Category	Count
Complexity	1

View more on Code Climate.

[netlify]

✅ Deploy Preview for jellyfishsdk ready!

Name	Link
🔨 Latest commit	886b8dc
🔍 Latest deploy log	https://app.netlify.com/sites/jellyfishsdk/deploys/63bbdb7c8c170b0008c68c25
😎 Deploy Preview	https://deploy-preview-1796--jellyfishsdk.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[codecov]

Codecov Report

Base: 91.44% // Head: 92.65% // Increases project coverage by +1.20% 🎉

Coverage data is based on head (886b8dc) compared to base (e2dc4ed).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1796      +/-   ##
==========================================
+ Coverage   91.44%   92.65%   +1.20%     
==========================================
  Files         367      367              
  Lines       10770    10772       +2     
  Branches     1378     1379       +1     
==========================================
+ Hits         9849     9981     +132     
+ Misses        887      761     -126     
+ Partials       34       30       -4     

Impacted Files	Coverage Δ
...ages/jellyfish-api-core/src/category/blockchain.ts	91.11% <100.00%> (+0.41%)	⬆️
...s/legacy-api/src/controllers/PoolPairController.ts	21.59% <0.00%> (-64.78%)	⬇️
packages/jellyfish-wallet-mnemonic/src/mnemonic.ts	63.63% <0.00%> (-36.37%)	⬇️
packages/jellyfish-address/src/script/P2WSH.ts	72.72% <0.00%> (-27.28%)	⬇️
...src/module.indexer/model/dftx/update.masternode.ts	75.67% <0.00%> (-24.33%)	⬇️
...ages/jellyfish-api-core/src/category/masternode.ts	84.00% <0.00%> (-16.00%)	⬇️
...ish-transaction/src/script/dftx/dftx_governance.ts	84.61% <0.00%> (-15.39%)	⬇️
...hale-api/src/module.api/poolpair.prices.service.ts	82.97% <0.00%> (-12.77%)	⬇️
...pi/src/module.indexer/model/dftx/composite.swap.ts	64.70% <0.00%> (-11.77%)	⬇️
packages/jellyfish-transaction/src/tx_composer.ts	71.66% <0.00%> (-8.34%)	⬇️
... and 43 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.