Disable pause indexing checkbox if a reindex is in progress

What does this MR do?

Related to #296884 (closed)

When Elasticsearch Zero-Downtime Reindexing task is in progress (the state of the task must be initial, indexing_paused, or reindexing), the Pause Elasticsearch indexing checkbox will now become disabled. It will re-enable when the task is complete (whether it is failed or succeeded).

How to test

Setup Advanced Search integration using Elasticsearch (including creating the index and enabling the index for searching)

• Navigate to Admin - Settings - Advanced Search
• Scroll to Elasticsearch zero-downtime reindexing
• Click the Trigger cluster reindexing button
• Refresh the screen to see the reindexing process move along
• Verify that the Pause Elasticsearch indexing checkbox gets disabled when the reindex task is in an in progress state (initial, indexing_paused, or reindexing)
• Verify that the Pause Elasticsearch indexing checkbox gets re-enabled when the reindexing task is done

Note: Once the reindexing is started, you can speed up the testing process by opening a rails console and initiating the ElasticClusterReindexingCronWorker manually

ElasticClusterReindexingCronWorker.perform_async

Screenshots (strongly suggested)

Disabled during a reindex

Does this MR meet the acceptance criteria?

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