Add ascopes/protobuf-maven-plugin to third_party.md (#16656)

This PR adds my project at https://github.com/ascopes/protobuf-maven-plugin to the thirdparty README.

CLA signed in previous contributions to other Google projects on GitHub.

Closes #16656

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/16656 from ascopes:patch-1 6f8b43aa0dd4da5a7bbf93460acd4094499aed2d
PiperOrigin-RevId: 629411565

Ashley committed 2y ago

2d56d69a40a4a13e1132be0ced546d0eed6ad2ad

Parent: c24e752

Committed by Copybara-Service <copybara-worker@google.com> on 4/30/2024, 2:54:44 PM