Improve the SQL reference including Search functions

[lukekim]

• Add proper index
• Add Scalar Functions

[github-actions]

✅ Pull with Spice Passed

Passing checks:

• ✅ Title meets minimum length requirement (10 characters)
• ✅ Has at least one of the required labels: area/blog, area/docs, area/cookbook, dependencies
• ✅ No banned labels detected
• ✅ Has at least one assignee: lukekim

[Copilot]

Pull Request Overview

This PR improves the SQL reference documentation by adding a dedicated SQL Reference index with scalar functions and a detailed table of contents while also cleaning up some outdated sections.

• Updated the navbar to include a link to the SQL Reference documentation and adjusted the announcement bar version.
• Removed outdated timestamp documentation and refined various SQL reference pages.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

File	Description
website/docusaurus.config.ts	Updated navbar links, announcement bar version changed, and removed the Community dropdown.
website/docs/reference/timestamp/index.md	Removed the outdated Timestamps documentation.
website/docs/reference/sql/*.md	Enhanced the SQL reference with a comprehensive table of contents and added Scalar Functions details.

Comments suppressed due to low confidence (2)

website/docusaurus.config.ts:118

• [nitpick] The removal of the 'Community' dropdown from the navbar appears unrelated to the SQL documentation improvements; consider double-checking if this removal was intended.

Removal of the 'Community' dropdown

website/docusaurus.config.ts:93

• The announcement bar's release version is updated to v1.2.0; please confirm that this change is intentional given the PR focus on SQL reference improvements.

content: '<a href="/blog/releases/v1.2.0">Spice.ai OSS v1.2.0</a> is now available! 🚀',

[peasee]

sql/index.md contains links to page anchors and/or sections that don't exist.

sql/scalar_functions.md contains a reference to array_has as an alias, but array_has is not defined in this document.

[github-actions]

🚀 deployed to https://51cc55bb.spiceai-org-website.pages.dev

[github-actions]

🚀 deployed to https://a6b8c2a8.spiceai-org-website.pages.dev

[github-actions]

🚀 deployed to https://62a8b712.spiceai-org-website.pages.dev

[github-actions]

🚀 deployed to https://2d81e0e0.spiceai-org-website.pages.dev