CBG-4677 restart db initialization if needed

[torcolvin]

If DatabaseInitManager is in the process of exiting due to context cancellation, and then another initialization process starts, that initialization will not start new workers but pick up the old workers instead.

The fix is to check to see if the context is cancelled when deciding whether restart workers.

Added WithCancelCause for debugging purposes to see which context was cancelled. The actual cancellation errors will appear in a RetryLoop for creating indexes.

Integration Tests

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGatewayIntegration/140/ (unrelated flake)

[Copilot]

Pull Request Overview

This PR addresses an issue where the DatabaseInitManager could pick up old, cancelled workers instead of starting new ones when database initialization is restarted. The fix involves checking if the worker's context is cancelled before reusing it and adding reason tracking for cancellation events.

• Adds context cancellation checking to prevent reusing shutdown workers
• Updates RemoveDatabase to accept a cancellation reason parameter
• Enhances error reporting for context cancellation with cause tracking

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rest/database_init_manager.go	Core fix: checks worker context cancellation before reuse and adds WithCancelCause support
rest/server_context.go	Updates RemoveDatabase signature to include reason parameter
rest/api.go	Updates RemoveDatabase calls with URL-based reasons
rest/admin_api.go	Updates RemoveDatabase and Cancel calls with descriptive reasons
rest/server_context_test.go	Updates test to use new RemoveDatabase signature
rest/replicatortest/replicator_test.go	Updates RemoveDatabase calls with test context descriptions
rest/indextest/index_init_api_test.go	Improves test assertions for better debugging
base/util.go	Updates RetryLoop to use context.Cause for better error reporting
base/util_test.go	Adds test coverage for context cancellation with cause