Modularise the NetworkOPs interface

[a1q123456]

High Level Overview of Change

This PR moves the NetworkOPs interface into libxrpl and it leaves the implementation in xrpld.

Context of Change

As the Change transaction directly replies on NetworkOPs, we have to move the interface to libxrpl before we can fully modularise transactors.

This PR is part of the modularisation of the transactors. See all PRs here:
#6222
#6223
#6224
#6225
#6226
#6227
#6228

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Performance (increase or change in throughput and/or latency)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

API Impact

• Public API: New feature (new methods and/or new fields)
• Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• Peer protocol change (must be backward compatible or bump the peer protocol version)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.2%. Comparing base (922752a) to head (f518dd5).

Additional details and impacted files

@@                         Coverage Diff                          @@
##           a1q123456/modularise-relational-db   #6225     +/-   ##
====================================================================
- Coverage                                79.2%   79.2%   -0.0%     
====================================================================
  Files                                     843     843             
  Lines                                   71694   71694             
  Branches                                 8284    8304     +20     
====================================================================
- Hits                                    56780   56758     -22     
- Misses                                  14914   14936     +22     

Files with missing lines	Coverage Δ
include/xrpl/server/InfoSub.h	100.0% <ø> (ø)
include/xrpl/server/NetworkOPs.h	100.0% <ø> (ø)
src/libxrpl/server/InfoSub.cpp	96.0% <ø> (ø)
src/xrpld/app/consensus/RCLConsensus.cpp	59.5% <ø> (ø)
src/xrpld/app/ledger/BookListeners.h	100.0% <ø> (ø)
src/xrpld/app/ledger/ConsensusTransSetSF.cpp	0.0% <ø> (ø)
src/xrpld/app/ledger/OrderBookDB.cpp	77.9% <ø> (ø)
src/xrpld/app/ledger/detail/InboundLedgers.cpp	36.0% <ø> (ø)
...rc/xrpld/app/ledger/detail/InboundTransactions.cpp	49.4% <ø> (ø)
src/xrpld/app/ledger/detail/LedgerMaster.cpp	41.6% <ø> (ø)
... and 29 more

... and 7 files with indirect coverage changes

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