Update Agent Builder landing page and get-started

[charlotte-hoblik]

This PR:

• Rewrites the landing page opening paragraph
• Name the default Elastic AI Agent in the get-started
• Add a tip about cloning the default agent as a starting point for custom agents

Context

These changes are the result of reviewing PM feedback on the Agent Builder
landing page (elastic-agent-builder.md) and get-started page (get-started.md).

Connected to: https://github.com/elastic/docs-content-internal/issues/855

[github-actions]

🔍 Preview links for changed docs

• explore-analyze/ai-features/agent-builder/get-started.md
• explore-analyze/ai-features/elastic-agent-builder.md

[github-actions]

Vale Linting Results

Summary: 1 warning, 1 suggestion found

⚠️ Warnings (1)

File	Line	Rule	Message
explore-analyze/ai-features/agent-builder/get-started.md	43	Elastic.QuotesPunctuation	Place punctuation inside closing quotation marks.

💡 Suggestions (1)

File	Line	Rule	Message
explore-analyze/ai-features/agent-builder/get-started.md	122	Elastic.Clone	Use clone only when referring to cloning a GitHub repository or creating a copy that is linked to the original. Often confused with 'copy' and 'duplicate'.

---

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To use Vale locally or report issues, refer to Elastic style guide for Vale.

[alaudazzi]

I know there isn't much we can do about it for now, but the crowd of applies-to in step 1 makes the formatting weird. You are tempted to resize the window to get them aligned :)

[leemthompo]

I know there isn't much we can do about it for now, but the crowd of applies-to in step 1 makes the formatting weird. You are tempted to resize the window to get them aligned :)

yep this is uggggly — but 9.4 should simplify things because AB will be enabled by default everywhere and we can collapse 9.3 stuff into a single tab or dropdown maybe

[leemthompo]

Few comments here one about formatting, and the other about trimming down the ingestion options a bit, and giving a bit more decision guidance :) LMKWYT

[leemthompo]

thx!