[Meta] Logstash use system indices API

[kaisecheng]

Elasticsearch introduced the System Indices and Hidden Indices concepts to replace indices that start with a dot, eg .logstash. These dot indices are an implementation detail that users should not interact with. Logstash centralized pipeline management uses .logstash to store pipeline information. It needed to migrate to the new System Indices API. (upstream: elastic/elasticsearch#50251)

Expected Tasks

• Logstash
  • Implement new endpoint (replace direct access of hidden indices with system indices api #12279)
  • [ ] Add integration test with multiple ES versions (7.9 and master)
• Kibana
  • Investigate permission handling
  • Investigate unmapped legacy API
  • Implement new endpoint (Update logstash pipeline management to use system index APIs kibana#80405)
  • [ ] Add integration test with multiple ES versions (7.9 and master)
• Documentation document system indices api privilege #12388 document system indices api privilege #12391

Future Tasks

After legacy API is deprecated

• clean up Logstash old implementation

[roaksoax]

Given that the work is now complete, going to go ahead and close this meta issue. I have filed #14660 to follow the remaining task.