Add setting up and loading data steps to prerequisites

[shoheichura]

Make clear that setting up and loading data steps are required for users using other adapters than BigQuery.

What are you changing in this pull request and why?

The current documentation is unclear as to Setting up and Loading data steps are required for users using other adapters than BigQuery such as Snowflake. I missed the prerequisite and got stuck in the quickstart guide myself. This pull request is to make clearer above steps are a prerequisite for every dbt adapter.

Checklist

• Review the Content style guide so my content adheres to these guidelines.
• For docs versioning, review how to version a whole page and version a block of content.
• Add a checklist item for anything that needs to happen before this PR is merged, such as "needs technical review" or "change base branch."

[welcome]

Hello!👋 Thanks for contributing to the dbt product documentation and opening this pull request! ✨
We use Markdown and some HTML to write the dbt product documentation. When writing content, you can use our style guide and content types to understand our writing standards and how we organize information in the dbt product docs.
We'll review your contribution and respond as soon as we can. 😄

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Name	Status	Preview	Comments	Updated (UTC)
docs-getdbt-com	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Dec 8, 2023 1:04pm

[mirnawong1]

hey @shoheichura thanks for opening up your first contribution to the docs and clarifying this! great callout and I'm happy to get this merged. looking forward to future contributions! ✨