docs: add pull-based-ingestion-bugfixes report for v3.4.0

[tkykenmt]

Summary

This PR adds documentation for pull-based ingestion bugfixes in OpenSearch v3.4.0.

Changes

Release Report: docs/releases/v3.4.0/features/opensearch/pull-based-ingestion-bugfixes.md

• Documents out-of-bounds offset handling fixes
• Documents removal of persisted pointers concept
• Documents file-based ingestion flaky test fix
• Explains migration notes for at-least-once processing guarantees

Feature Report Update: docs/features/opensearch/pull-based-ingestion.md

• Added v3.4.0 PRs to Related PRs table
• Added v3.4.0 issues to References
• Added v3.4.0 entry to Change History
• Marked totalDuplicateMessageSkippedCount metric as deprecated
• Added at-least-once limitation note

Release Index Update: docs/releases/v3.4.0/index.md

• Added link to pull-based ingestion bugfixes report

Related PRs

• [Pull-based Ingestion] Fix poller bug and remove persisted pointers opensearch-project/OpenSearch#19607: Fix pull-based ingestion out-of-bounds offset scenarios
• Fix file-based ingestion flaky test opensearch-project/OpenSearch#19757: Fix file-based ingestion consumer start point handling

Related Issue

• Closes #1709