Add refresh interval and bulk indexing response info

[shainaraskas]

fixes #1643

• added a callout that the default values and constraints on settings might be different in serverless
• added bulk indexing as a supported feature, with a note that the minimum response time is fixed for serverless (let me know if you have any better ideas on how to communicate this one on the differences page 💡)
• Added a note about the min response time of bulk indexing in the indexing speed tuning page to better set expectations around tuning

added @leemthompo as a reviewer because he knows the differences page well and might have some ideas

made some complimentary changes to:

• the api reference
• the settings reference

[github-actions]

🔍 Preview links for changed docs

• deploy-manage/deploy/elastic-cloud/differences-from-other-elasticsearch-offerings.md
• deploy-manage/production-guidance/optimize-performance/indexing-speed.md

[yetanothertw]

LGTM! 🐈

[leemthompo]

lgtm, with a potentially superfluous doc link suggestion :)