Augment vector search tutorial with getting started content

[lcawl]

This PR:

• ports content from https://www.elastic.co/getting-started/enterprise-search/vector-search into the existing https://www.elastic.co/docs/solutions/search/vector/bring-own-vectors page
• adds a link to that page from the Elasticsearch getting started section
• aligns some terminology (e.g. "create a vector database", "test a vector search") and style ("prequisites" section, use of stepper component) with what was done in the semantic search quickstart

[github-actions]

🔍 Preview links for changed docs:

• solutions/search/serverless-elasticsearch-get-started-vector.md

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[github-actions]

🔍 Preview links for changed docs

• solutions/search/get-started/quickstarts.md
• solutions/search/vector/bring-own-vectors.md

[leemthompo]

Nothing but nits from me 😄