Support rolling upgrades to OpenSearch 1.0 from ODFE 1.13 and ES 7.10.x

[dblock]

Upgrading your cluster from ElasticSearch to OpenSearch and OpenSearch Dashboards is just like upgrading your cluster between versions of ElasticSearch and Kibana. Specifically, OpenSearch supports rolling upgrades and restart upgrades from ElasticSearch 6.8.0 through ElasticSearch 7.10.2 and to OpenSearch 1.0. OpenSearch Dashboards supports restart upgrades from Kibana 6.8.0 through Kibana 7.10.2 and to OpenSearch Dashboards 1.0.

• OpenSearch Dashboards, see Support restart upgrades to OpenSearch Dashboards 1.0 from Kibana v7.10.x OpenSearch-Dashboards#334.
• OpenSearch Plugins, see Support rolling upgrades for OpenSearch plugins, and restart upgrades for OpenSearch Dashboards Plugins 1.0 opensearch-plugins#12.
• OpenSearch itself, see [BUG] Meta issue to track all places we have broken backwards compatibility in OpenSearch 1.0.0-beta1 #640.
• Upgrade/migration guide, Document/create/add a migration guide from ES 7.10.2 #801

We have asked the community regarding the upgrade path to OpenSearch. Please continue adding your comments.

Additional context

[saratvemulapalli]

For OpenSearch we still have to understand what we have broken and what needs to be backwards compatible.
For example plugins we have already figure out these are the ones to take care of: opensearch-project/opensearch-plugins#12

Here is an issue we opened to track them and I am confident this just scratching the surface: #640

[saratvemulapalli]

Pasting it back from the earlier issue since this is important.
These are all the items which we should consider while working on the drop in upgrades.

Ordering of upgrading
Naming conventions
Upgrade time-lag (aka downtime)
Replication
Security
Downstream Dependencies
Upgrade alerting and notifications
Limits
Performance
Availability
Latency
Compatibility Matrix
Downgrade
APIs

[nknize]

Can we convert this into a meta issue and track incremental issues the community can help pick off?