New cross db macros

[dbeatty10]

closes #2049

Description & motivation

• Document new cross-database macros.
• Add dbt. namespace prefix to all code examples

Prerelease docs

If this change is related to functionality in a prerelease version of dbt:

• I've added versioning components, as described in "Versioning Docs"
• I've added a note to the prerelease version's Migration Guide

[netlify]

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[dbeatty10]

Update: This is SOLVED 🙏

@matthewshaver could you or someone else on the docs team help me troubleshoot something?

Do version blocks work with the Netflify deploy preview?

Here's why I ask...

Goal

My goal is to version the content of website/docs/reference/dbt-jinja-functions/cross-database-macros.md:

• The majority of the page should first be available in version 1.2
• This PR is intended to add a few new blocks of code first available in version 1.3
• (If possible) no content of this page should be available before 1.2

Problem

The problem I'm experiencing:

• This entire page is already versioned per these instructions
• I tried to add version blocks per these instructions
• But when I look at the deploy preview here, no content changes dynamically when I change the version number