[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

[kunisen]

@eedugon thanks for your great work! this is awesome and I love it!
I read thru the PR in a high level and it looks great!

Only one small thing, personal feeling, I found the badge serverless is a bit hard to find, given it's the same "text" but not really like a badge... 😅
Maybe not in this PR, but in the long run, could we improve the badge to make it move visible? e.g. make it an icon or make the badge a different color?

[shainaraskas]

@kunisen we are working on the badge designs with UX now. We need to balance badge visibility with making the page too noisy (because we use these same badges everywhere), but you'll see changes to that experience in the coming months as our eng team finds time to address :)