Add nftoken_id, nftoken_ids, and offer_id fields to TransactionMetadata

[nkramer44]

Fixes #435

Also adds index field to NfTokenObject so users can get the NFToken ID when calling account_nfts or account_objects

[codecov[bot]]

Codecov Report

Merging #463 (d5063bf) into main (75dd383) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #463   +/-   ##
=========================================
  Coverage     90.46%   90.46%           
  Complexity     1468     1468           
=========================================
  Files           287      287           
  Lines          4174     4174           
  Branches        339      339           
=========================================
  Hits           3776     3776           
  Misses          277      277           
  Partials        121      121           

Files Changed	Coverage Δ
...g/xrpl/xrpl4j/model/ledger/NfTokenOfferObject.java	100.00% <ø> (ø)
...xrpl4j/model/transactions/TransactionMetadata.java	100.00% <ø> (ø)