Add nonce JSON-RPC endpoint

[insipx]

Adds a nonce endpoint in order to sign setAttribute payloads in libxmtp and xps-cli

• adds documentation for walletAddress
• fixes docs in some places
• adds nonce endpoint & tests
• tests for resolve_did_address

closes #63

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (65634b5) 76.43% compared to head (39105d8) 78.75%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #72      +/-   ##
==========================================
+ Coverage   76.43%   78.75%   +2.31%     
==========================================
  Files          13       14       +1     
  Lines         522      579      +57     
==========================================
+ Hits          399      456      +57     
  Misses        123      123              

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[37ng]

lgtm
not in the scope of this pr - I think our doc could be more concise and omit information that could be found in JSON-RPC 2.0 Specification

[jac18281828]

All looks good! Thanks for adding this