feat: add CAP-71 (Protocol 27) Soroban authorization support

[overcat]

#803

[codecov]

Codecov Report

❌ Patch coverage is 86.82635% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.88%. Comparing base (4025b8e) to head (2cb9f1e).

Files with missing lines	Patch %	Lines
src/main/java/org/stellar/sdk/Auth.java	89.11%	8 Missing and 8 partials ⚠️
...org/stellar/sdk/contract/AssembledTransaction.java	14.28%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #804      +/-   ##
============================================
+ Coverage     82.76%   82.88%   +0.11%     
- Complexity     1621     1660      +39     
============================================
  Files           232      232              
  Lines          5937     6060     +123     
  Branches        657      678      +21     
============================================
+ Hits           4914     5023     +109     
- Misses          653      660       +7     
- Partials        370      377       +7     

Files with missing lines	Coverage Δ
src/main/java/org/stellar/sdk/Sep45Challenge.java	79.23% <100.00%> (+0.88%)	⬆️
...org/stellar/sdk/contract/AssembledTransaction.java	43.27% <14.28%> (+0.74%)	⬆️
src/main/java/org/stellar/sdk/Auth.java	85.42% <89.11%> (+1.88%)	⬆️

... and 1 file with indirect coverage changes

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