ledger: add kvIter to storage package (11 of N)

[icorderi]

Summary

Handles the last remaining queries left in ledger used in production code.
A few sql statements remain in specific tests.

Previous parts of this refactor:

• part 1 - ledger: move pieces of accountdb.go into a storage package #4776
• part 2 - ledger: move catchpoint sql code into storage package #4813
• part 3 - ledger: move non-lookup methods into a storage package #4830
• part 4 - ledger: move catchpoint related methods into a storage package #4835
• part 5 - ledger: move catchpoint staging into a storage package (5 of N) #4836
• part 6 - ledger: move blockdb into a storage package (6 of N) #4841
• part 7 - ledger: move migrations into a storage package (7 of N) #4846
• part 8 - ledger: move blockdb tests into a storage package (8 of N) #4860
• part 9 - ledger: new db methods to abstract queries needed by the deltas (9 of N) #4864
• part 10 - ledger: move iterators into a store package (10 of N) #4874

What remains to be moved out:

• misc queries left in ledger
  • acctdeltas_test.go
  • acctupdates_test.go
  • catchpointtracker.go
  • catchpointwriter.go
  • catchpointwriter_test.go

Test Plan

Existing tests.

[codecov]

Codecov Report

Merging #4892 (37db992) into master (8cb6779) will decrease coverage by 0.04%.
The diff coverage is 20.00%.

@@            Coverage Diff             @@
##           master    #4892      +/-   ##
==========================================
- Coverage   53.69%   53.64%   -0.05%     
==========================================
  Files         430      431       +1     
  Lines       53529    53536       +7     
==========================================
- Hits        28741    28722      -19     
- Misses      22560    22586      +26     
  Partials     2228     2228              

Impacted Files	Coverage Δ
ledger/store/kvsIter.go	0.00% <0.00%> (ø)
ledger/catchpointtracker.go	58.49% <50.00%> (+0.15%)	⬆️
ledger/catchpointwriter.go	59.37% <100.00%> (-0.63%)	⬇️
ledger/blockqueue.go	85.63% <0.00%> (-2.88%)	⬇️
network/wsPeer.go	67.06% <0.00%> (-1.91%)	⬇️
catchup/service.go	69.08% <0.00%> (-1.45%)	⬇️
network/wsNetwork.go	64.92% <0.00%> (-0.27%)	⬇️
data/transactions/verify/txn.go	74.57% <0.00%> (+0.84%)	⬆️
ledger/roundlru.go	96.22% <0.00%> (+5.66%)	⬆️

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