fix: [DevOps] Japicmp use orchestration-staging as baseline

[rpanackal]

Context

AI/ai-sdk-java-backlog#ISSUENUMBER.

Changing the narative of the Japicmp check from

Is the newly generated orchestration JAR compatible with main?

towards

Is the newly generated orchestration JAR compatible with the currently accepted orchestration api?

• Here "currently accepted orchestration api" assumes orchestration-staging branch contains fixes that are human-reviewed and accepted.

Without this change, orchestration PRs that already has a fix ready will keep failing since the defacto baseline is main. This is just noisy since some team member already looked at the problem, fixed it and created orchestration-staging. Without this, every upcoming orchestration PRs will always fail too.

Feature scope:

• Use orchestration-staging as baseline if it exists

Definition of Done

• Functionality scope stated & covered
• Tests cover the scope above
• Error handling created / updated & covered by the tests above
• Aligned changes with the JavaScript SDK
• Documentation updated
• Release notes updated