CORE-69: remove explicit dependency on snakeyaml

[davidangb]

Jira: https://broadworkbench.atlassian.net/browse/CORE-69

Removes the explicit dependency on snakeyaml. This supersedes #311.

When pulled in transitively, without the explicit dependency declaration, snakeyaml is at version 2.3:

---

• Submitter: Make sure Swagger is updated if API changes
• Submitter: If updating admin endpoints, also update firecloud-admin-cli
• Submitter: Update FISMA documentation if changes to:
  • Authentication
  • Authorization
  • Encryption
  • Audit trails
• Submitter: If you're adding new libraries, sign us up to security updates for them

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.71%. Comparing base (31a75e6) to head (5364164).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #354   +/-   ##
========================================
  Coverage    59.71%   59.71%           
========================================
  Files           18       18           
  Lines          638      638           
  Branches        66       66           
========================================
  Hits           381      381           
  Misses         257      257           

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