Restructure Core/Enterprise getting started docs

[sanderson]

• Breaks the Core and Enterprise getting started documentation into smaller, focused pages
• Adds information about managing file indexes Enterprise
• Creates a doc specifically for multi-node Enterprise clusters
• Splits the HTTP API and Client library docs into two separate pages

---

• Rebased/mergeable

[Copilot]

Pull Request Overview

This PR restructures the Core and Enterprise getting started documentation by splitting larger pages into focused documents, adding new content for multi-node clusters and file indexing, and updating the HTTP API and client library docs.

• Updated titles, aliases, and menu identifiers for consistency.
• Introduced new documentation pages for write, setup, query, and processing-engine topics.
• Removed obsolete CLI reference files and added new content for managing file indexes.

Reviewed Changes

Copilot reviewed 40 out of 40 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
content/influxdb3/enterprise/write-data/client-libraries.md	Updated title, menu name, and source alias for clarity.
content/influxdb3/enterprise/reference/config-options.md	Added code block closure to improve formatting.
content/influxdb3/enterprise/install/_index.md	Added a multi-node cluster link and children shortcode.
content/influxdb3/enterprise/get-started/*.md	New getting started guides for write, setup, query, and processing-engine.
content/influxdb3/enterprise/admin/file-index/*.md	New guides for creating, deleting, and managing file indexes.
content/influxdb3/core/write-data/http-api/*.md & client-libraries.md	Updated titles, menu items, and source paths for consistency.
content/influxdb3/core/reference/cli/influxdb3/*file_index.md	Removed obsolete files.
content/influxdb3/core/get-started/*.md	New getting started guides for write, setup, query, and processing-engine.

Comments suppressed due to low confidence (3)

content/influxdb3/enterprise/get-started/processing-engine.md:23

• The source comment incorrectly references 'query.md' instead of 'processing-engine.md'; please update the comment to match the correct source file.

// SOURCE content/shared/influxdb3-get-started/query.md

content/influxdb3/core/get-started/processing-engine.md:23

• The source comment incorrectly references 'query.md' rather than 'processing-engine.md'; please update it to reflect the accurate source location.

// SOURCE content/shared/influxdb3-get-started/query.md

content/influxdb3/enterprise/reference/config-options.md:257

• [nitpick] Verify that the added code block closure has a matching opening fence to maintain proper markdown formatting.

</details>

[jstirnaman]

@MeelahMe Can you point me to where you found this variable?

[jstirnaman]

@MeelahMe We shouldn't add this in Setup--it's a little misleading and too much detail that isn't directly related; it distracts from the basic goal of the page.