Discovery API: update docs

[eddowh]

What are you changing in this pull request and why?

I'm updating the docs of Discovery API because we have breaking changes to the API and we need to update the docs to better reflect the current state of our API, since the docs point to legacy endpoints we plan to deprecate soon.

• update use case queries to use bigints and new apis
• update other queries to use bigints and new apis
• docs parity with legacy vs new endpoints
• fix bug where schemas and types weren't retrieved properly
• update or remove screenshots (we're keeping it)
• verify that Python code works (no bandwidth -- if it breaks it breaks, not the most urgent for getting docs out)

Some common mistakes I found while going through each query and executing it to make sure it's valid.

• Fields were snake_case when they should be camelCase
• Typos in filters and fields
• Nested nodes were not updated so ... on syntaxes were invalid
• Querying non-nested-allowed fields of a nested node, like children, tests, etc.

Checklist

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

(Below might be a separate PR, but leaving it for now)

Adding new pages (delete if not applicable):

• Add page to website/sidebars.js
• Provide a unique filename for the new page

Removing or renaming existing pages (delete if not applicable):

• Remove page from website/sidebars.js
• Add an entry website/static/_redirects
• Ran link testing to update the links that point to the deleted page

[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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