[INFRA-8096] Migrate to GHA

[areuge]

https://urbanairship.atlassian.net/browse/INFRA-8229

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What does this do and why?

This PR migrates the CI/CD release and testing pipelines from Jenkins to standalone GitHub Actions workflows (INFRA-8096), aligning the deployment architecture with the main java-library repository.

Additional notes for reviewers

more info in ticket

Testing

• If these changes added new functionality, I tested them against the live API with real auth
• I wrote tests covering these changes
• I ran the full test suite and it passed

Test run results, including date and time:

Result: BUILD SUCCESS — All 56 tests executed and passed cleanly via the GitHub Actions runner.

Airship Contribution Agreement

Link here

• I've filled out and signed Airship's contribution agreement form.

Screenshots

• If applicable