Clarify hardware profile and instance configuration related docs for ECH

[kunisen]

Background

There are a bunch of hardware profile and instance configuration related ECH docs that are not clear enough and have caused some confusions to users and support so far.
After syncing with @yuvielastic @maggieghamry @stefnestor and @jakommo, we decided to make some doc updates to clarify.

Details in this internal ticket (https://github.com/elastic/support-tech-lead/issues/1586). Below is a quick recap of what we would like to change.

For reviewers

• Requested @yuvielastic your kind review from PM's perspective
• Requested @claudia-correia your kind review from engineering's perspective
• Requested @maggieghamry your kind review from support's perspective
• Requested @eedugon or @shainaraskas your kind review from docs team's perspective

Recap of what to change

:: [1]

https://www.elastic.co/docs/deploy-manage/deploy/elastic-cloud/ec-change-hardware-profile

• Change title to Manage hardware profiles
• Add that version <= 7.10 can't do hardware profile migration

:: [2]

https://www.elastic.co/docs/deploy-manage/deploy/elastic-cloud/change-hardware

• Update the doc from mentioning "Change hardware" to "Customize instance configuration" and make this update all through this doc page. <= It's technically more proper to say "instance configuration" but not just "hardware"
• Add "Hardware profile is also referenced as deployment templates (DTs) in ECH to make it more logically connectable"
• Add an "In addition" paragraph to explain some details, that has confused users and support so far. We have already confirmed with Yuvi from technical perspective.

:: [3]

https://www.elastic.co/docs/deploy-manage/production-guidance/optimize-performance/search-speed

• Reference regarding "hardware profile" is not correct. It should be the real hardware profile one as mentioned in [1].

:: [4]

https://www.elastic.co/docs/deploy-manage/production-guidance/optimize-performance/indexing-speed

• Reference regarding "hardware profile" is not correct. It should be the real hardware profile one as mentioned in [1].

:: [5]

Move https://www.elastic.co/docs/deploy-manage/deploy/elastic-cloud/change-hardware - "customize IC" doc under https://www.elastic.co/docs/deploy-manage/deploy/elastic-cloud/ec-change-hardware-profile "manage hardware profile" to make it more logically clear.

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🔍 Preview links for changed docs

• deploy-manage/deploy/elastic-cloud/ec-change-hardware-profile.md
• deploy-manage/deploy/elastic-cloud/change-hardware.md
• deploy-manage/production-guidance/optimize-performance/indexing-speed.md
• deploy-manage/production-guidance/optimize-performance/search-speed.md

---

cc @maggieghamry @stefnestor @jakommo

[github-actions]

🔍 Preview links for changed docs

• deploy-manage/deploy/elastic-cloud/change-hardware.md
• deploy-manage/deploy/elastic-cloud/ec-change-hardware-profile.md
• deploy-manage/production-guidance/optimize-performance/indexing-speed.md
• deploy-manage/production-guidance/optimize-performance/search-speed.md