[AMORO-4447][CI] Prevent multiple assignees from take comments

[sivakumar-mahalingam]

Why are the changes needed?

The issue-assignment workflow used the additive addAssignees API for every take comment. As a result, multiple users could be assigned when they commented take on the same issue.

The workflow should assign only the first user who claims an unassigned issue. Subsequent take comments must not change its assignees.

Close #4447.

Brief change log

• Fetch the latest issue state and ignore take comments when the issue is already assigned.
• Find the earliest exact take comment and assign only its author.
• Prevent concurrent workflow runs from assigning multiple users.
• Await the GitHub assignment API call so failures are reported.
• Update CONTRIBUTING.md to document the first-claim behavior.

How was this patch tested?

• Tested the embedded workflow script with mocked GitHub API scenarios covering the first claim, subsequent claims, an already-assigned issue, and concurrent claims.
• Add screenshots for manual tests if appropriate (not applicable).
• Ran actionlint .github/workflows/take.yml.
• Ran git diff --check.
• Ran ./mvnw validate successfully for all 33 modules.

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[sivakumar-mahalingam]

take