Document how to use to the elasticsearch-node tool

[pebrc]

The elasticsearch-node command enables you to perform certain unsafe operations on a node that are only possible while it is shut down. This command allows you to adjust the role of a node, unsafely edit cluster settings and may be able to recover some data after a disaster or start a node even if it is incompatible with the data on disk.

We should document how to use the tool in an ECK context e.g. how to set up the correct init containers etc. We could use this discuss topic as a starting point

[pebrc]

Closing as the approach in the linked discuss issue has too many disadvantages. Specifically the fact that the code in the initcontainer will run multiple times and have a destructive effect on the cluster makes this not something we should recommend in our documenation.

I have raised #4546 to explore are more robust approach.