[Docs] Includes information about available index settings in Serverless

[eedugon]

This Docs PR starts addressing elastic/docs-content#79

The main change is to introduce and show the list of index-level settings available in Serverless. For this purpose:

• A new page with the list of available index settings has been created.
• In the index-settings landing page and all relevant child pages:
  • Banner explaining that not all settings are available in serverless.
  • Serverless badges in relevant settings, next to the name.

Some screenshots for ilustrative purposes:

• The refresh_interval setting has been updated as it has a different default in serverless.

There are other minor changes / refinement done while reviewing all the content, such as:

• Some links to dynamic index settings were pointing to the cluster settings API doc. Fixed.
• Some items of the index settings hierarchy were not correctly placed under shard allocation section.
• The landing page and the general index settings had some inconsistencies with the concept index modules.
• The TOC order of the index settings section has been updated to look a bit closer to the previous docs.

[github-actions]

🔍 Preview links for changed docs:

• docs/reference/elasticsearch/configuration-reference/data-stream-lifecycle-settings.md
• docs/reference/elasticsearch/configuration-reference/index-lifecycle-management-settings.md
• docs/reference/elasticsearch/configuration-reference/index.md
• docs/reference/elasticsearch/index-settings/data-tier-allocation.md
• docs/reference/elasticsearch/index-settings/history-retention.md
• docs/reference/elasticsearch/index-settings/index-block.md
• docs/reference/elasticsearch/index-settings/index-modules.md
• docs/reference/elasticsearch/index-settings/index.md
• docs/reference/elasticsearch/index-settings/mapping-limit.md
• docs/reference/elasticsearch/index-settings/merge.md
• docs/reference/elasticsearch/index-settings/preloading-data-into-file-system-cache.md
• docs/reference/elasticsearch/index-settings/recovery-prioritization.md
• docs/reference/elasticsearch/index-settings/serverless.md
• docs/reference/elasticsearch/index-settings/shard-allocation.md
• docs/reference/elasticsearch/index-settings/similarity.md
• docs/reference/elasticsearch/index-settings/slow-log.md
• docs/reference/elasticsearch/index-settings/sorting-conjunctions.md
• docs/reference/elasticsearch/index-settings/sorting.md
• docs/reference/elasticsearch/index-settings/store.md
• docs/reference/elasticsearch/index-settings/time-series.md
• docs/reference/elasticsearch/index-settings/total-shards-per-node.md
• docs/reference/elasticsearch/index-settings/translog.md
• docs/reference/elasticsearch/mapping-reference/analyzer.md
• docs/reference/elasticsearch/mapping-reference/coerce.md
• docs/reference/elasticsearch/mapping-reference/ignore-malformed.md
• docs/reference/elasticsearch/mapping-reference/index-mapping-ignore-above.md
• docs/reference/elasticsearch/mapping-reference/mapping-source-field.md

🔔 The preview site may take up to 3 minutes to finish building. These links will become live once it completes.

[shainaraskas]

indexing pressure is missing a note

[shainaraskas]

is path in totally the wrong place??? also maybe indexing pressure I guess

[shainaraskas]

overall, looks really good.

when i saw the mapping/metadata fields were impacted I got a little nervous - do those references need an overall note on them? wondering how much of the content is deployment-agnostic and how much of it follows this restriction pattern.

approving to unblock

[elasticsearchmachine]

Pinging @elastic/es-docs (Team:Docs)

[shainaraskas]

I typed these comments days ago and forgot to submit

[john-wagster]

lgtm

[eedugon]

I typed these comments days ago and forgot to submit

I've updated the serverless introductory paragraph due to that. Very good point, now it's aligned with the upcoming change in elastic/docs-content#1728