Add receivingChainID request param support to transactions endpoint

[vardan10]

What was the problem?

This PR resolves #1931

How was it solved?

• Added support for receivingChainID to be currentChainID in transactions API
• Fix TODOs
• /transactions endpoint now returns pending transactions by default

How was it tested?

Local

[codecov]

Codecov Report

Merging #1934 (2a96a5d) into release/0.7.0 (4735a6d) will increase coverage by 0.02%.
The diff coverage is 85.71%.

Additional details and impacted files

@@                Coverage Diff                @@
##           release/0.7.0    #1934      +/-   ##
=================================================
+ Coverage          67.71%   67.74%   +0.02%     
=================================================
  Files                299      299              
  Lines               5290     5301      +11     
  Branches             968      973       +5     
=================================================
+ Hits                3582     3591       +9     
- Misses              1708     1710       +2     

Files	Coverage Δ
...ervice/business/interoperability/blockchainApps.js	77.55% <ø> (ø)
...e/business/interoperability/blockchainAppsStats.js	48.38% <ø> (ø)
...shared/dataService/business/pendingTransactions.js	92.94% <100.00%> (+0.63%)	⬆️
...indexer/shared/dataService/business/pos/stakers.js	18.64% <ø> (+0.61%)	⬆️
...exer/shared/dataService/business/pos/validators.js	95.55% <ø> (ø)
...lockchain-indexer/shared/dataService/generators.js	26.08% <ø> (ø)
...chain-indexer/shared/dataService/pos/validators.js	24.04% <ø> (ø)
...gateway/apis/http-version3/methods/transactions.js	100.00% <ø> (ø)
services/gateway/shared/paramValidator.js	100.00% <100.00%> (ø)
services/gateway/shared/registerHttpApi.js	98.98% <ø> (ø)
... and 3 more

... and 1 file with indirect coverage changes

[sameersubudhi]

The fixes seem to work as expected, except for the issue reported in #1937.