Cloud-on-k8s: Write Elasticsearch Spec documentation

[sebgl]

Should cover advanced usage such as:

• SetVMMaxMapCount
• Set JVM heap size
• Resource limits
• Volume claim templates
• Node configuration
• Pod Template
• Setup init containers for plugin downloads
• Pod disruption budget
• Change budget (maxUnavailable, maxSurge)
• HTTP settings & TLS SANs
• Custom HTTP cert
• Secure settings
• Custom plugins and bundles

[avloss]

Could this also cover how to disable password?

[pebrc]

Let's break this down into smaller issues that could be worked on in parallel

[alaudazzi]

After discussion with @sebgl, this documentation task is reorganised in two main sections, with relevant topic contributors:

How to configure your cluster

Put a general introduction here [@alaudazzi]

Add a description for each feature and integrate one or more examples.

Basic features (features everyone should know about)

• [x] Set JVM heap size [@david-kow ]
• [x] Resource limits [@barkbay]
• [x] Volume claim templates [@barkbay]
• [x] Node configuration [@thbkrkr] (possible overlapping with https://github.com/elastic/cloud-on-k8s/issues/1143)
• [ ] Pod Template [@jonsabo ]
• [x] HTTP settings & TLS SANs [@thbkrkr]
  (examples for this feature already exist in https://www.elastic.co/guide/en/cloud-on-k8s/master/k8s-accessing-elastic-services.html)

Advanced features (features for experienced users)

• [x] [SetVMMaxMapCount ](https://github.com/elastic/cloud-on-k8s/issues/970)[@artemnikitin ]
• [x] Setup init containers for plugin downloads [@pebrc]
• [x] Pod disruption budget [@sebgl ]
• [x] Change budget (maxUnavailable, maxSurge) [@sebgl]
• [x] Custom HTTP cert [@thbkrkr]
• [x] [Secure settings](https://github.com/elastic/cloud-on-k8s/issues/997) [@pebrc]
• [x] Custom plugins and bundles [@pebrc]

[pebrc]

I have updated the break down to include all team members. Feel free to start working on those sections.

[alaudazzi]

Completed the doc reorg and editing in #1421.