Add pending token airdrops to REST API

[edwin-greene]

Description: Adds the pending token airdrops endpoint to the REST API.

Related issue(s):

Fixes #8282

Notes for reviewer: This PR only adds support for Fungible Tokens. NFTs will be added in a future PR.

Checklist

• [x] Documented (Code comments, README, etc.)
• [x] Tested (unit, integration, etc.)

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.56%. Comparing base (b2349db) to head (2a1189c). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #9383 +/- ## ========================================= Coverage 92.55% 92.56% - Complexity 7039 7041 +2 ========================================= Files 912 913 +1 Lines 29760 29772 +12 Branches 3760 3759 -1 ========================================= + Hits 27544 27558 +14 Misses 1445 1445 + Partials 771 769 -2 ```

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