[esArchiver] log when migrations complete and we're done loading data

[spalger]

I'm tracking a likely upcoming source of flakiness, probably caused by #85778

I'm 50% sure this issue is in the esArchiver, and I'd like to avoid reverting that massive PR, so I'm looking to do some logging that helps us identify what is causing failures like https://kibana-ci.elastic.co/job/elastic+kibana+pipeline-pull-request/102742/execution/node/965/log/

14:56:00                 │ proc [kibana]   log   [21:56:00.450] [info][savedobjects-service] [.kibana] Migration completed after 185ms
14:56:56                 │ proc [kibana]   log   [21:56:53.930] [error][plugins][taskManager] [WorkloadAggregator]: Error: Invalid workload: {"took":0,"timed_out":false,"_shards":{"total":0,"successful":0,"skipped":0,"failed":0},"hits":{"total":{"value":0,"relation":"eq"},"max_score":0,"hits":[]}}
14:56:57                 │ proc [kibana]   log   [21:56:57.210] [warning][collector-set][plugins][usageCollection] ResponseError: index_not_found_exception
14:56:57                 │ proc [kibana]     at onBody (/dev/shm/workspace/kibana-build-xpack-4/node_modules/@elastic/elasticsearch/lib/Transport.js:333:23)
14:56:57                 │ proc [kibana]     at IncomingMessage.onEnd (/dev/shm/workspace/kibana-build-xpack-4/node_modules/@elastic/elasticsearch/lib/Transport.js:260:11)
14:56:57                 │ proc [kibana]     at IncomingMessage.emit (events.js:327:22)
14:56:57                 │ proc [kibana]     at endReadableNT (internal/streams/readable.js:1327:12)
14:56:57                 │ proc [kibana]     at processTicksAndRejections (internal/process/task_queues.js:80:21) {
14:56:57                 │ proc [kibana]   meta: {
14:56:57                 │ proc [kibana]     body: { error: [Object], status: 404 },
14:56:57                 │ proc [kibana]     statusCode: 404,
14:56:57                 │ proc [kibana]     headers: {
14:56:57                 │ proc [kibana]       'content-type': 'application/json;charset=utf-8',
14:56:57                 │ proc [kibana]       'content-length': '449'
14:56:57                 │ proc [kibana]     },
14:56:57                 │ proc [kibana]     meta: {
14:56:57                 │ proc [kibana]       context: null,
14:56:57                 │ proc [kibana]       request: [Object],
14:56:57                 │ proc [kibana]       name: 'elasticsearch-js',
14:56:57                 │ proc [kibana]       connection: [Object],
14:56:57                 │ proc [kibana]       attempts: 0,
14:56:57                 │ proc [kibana]       aborted: false
14:56:57                 │ proc [kibana]     }
14:56:57                 │ proc [kibana]   }
14:56:57                 │ proc [kibana] }
14:56:57                 │ proc [kibana]   log   [21:56:57.216] [warning][collector-set][plugins][usageCollection] Unable to fetch data from core collector
14:58:04                 │ proc [kibana]   log   [21:57:53.935] [error][plugins][taskManager] [WorkloadAggregator]: Error: Invalid workload: {"took":0,"timed_out":false,"_shards":{"total":0,"successful":0,"skipped":0,"failed":0},"hits":{"total":{"value":0,"relation":"eq"},"max_score":0,"hits":[]}}
14:58:04                 └- ✖ fail: saved objects tagging API DELETE /api/saved_objects_tagging/tags/{id} "before each" hook for "should delete the tag"
14:58:04                 │      Error: Timeout of 360000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/dev/shm/workspace/parallel/4/kibana/x-pack/test/saved_object_tagging/api_integration/tagging_api/apis/delete.ts)
14:58:04                 │       at listOnTimeout (internal/timers.js:554:17)
14:58:04                 │       at processTimers (internal/timers.js:497:7)

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[spalger]

esArchiver is functional, this is a tiny change and we could use it for debugging now so I'm going to merge early.

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: cda0994

Metrics [docs]

✅ unchanged

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[kibanamachine]

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