dns cache settings page moved to ES configuration section

[eedugon]

Moving DNS cache settings content from important system configuration to Important settings configuration section.

The important system configuration section is intended for OS settings that need to be configured before installing Elasticsearch, and the DNS cache settings page is a post-installation config item and not even an OS setting.

The content was originally an indivitual page and we are integrating the content into the "important settings configuration" section.

In a separate PR we should also place the content into Elasticsearch reference docs, same as the rest of that page.

Related issue: #3007

[github-actions]

🔍 Preview links for changed docs

• deploy-manage/deploy/self-managed/important-settings-configuration.md
• deploy-manage/deploy/self-managed/important-system-configuration.md
• deploy-manage/distributed-architecture/discovery-cluster-formation/discovery-hosts-providers.md

[shainaraskas]

Maybe we should move the content to Elasticsearch reference docs, same as GC logging settings?

I think the settings should be duplicated to the JVM setting reference to keep both sets of content complete.

the only reason i'd put it only in the reference is if the relative importance of setting it is reduced

[shainaraskas]

lgtm