Link to the environment variables that are available for setting (#5449)

[Preview](https://docs-getdbt-com-git-dbeatty10-patch-1-1-dbt-labs.vercel.app/reference/global-configs/environment-variable-configs)

## What are you changing in this pull request and why?

The [project
flags](https://docs.getdbt.com/reference/global-configs/project-flags)
has a link to the [table of all
flags](https://docs.getdbt.com/reference/global-configs/about-global-configs#available-flags),
so it seems like the [environment variables
page](https://docs.getdbt.com/reference/global-configs/environment-variable-configs)
should as well.

## Checklist
- [x] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
so my content adheres to these guidelines.

---------

Co-authored-by: Ly Nguyen <[email protected]>

website/docs/reference/global-configs/environment-variable-configs.md

@@ -4,7 +4,7 @@ id: "environment-variable-configs"
 sidebar: "Environment variable configs"
 ---
 
-Environment variables contain a `DBT_` prefix
+Environment variables contain a `DBT_` prefix. For a list of all dbt environment variables you can set, refer to [Available flags](/reference/global-configs/about-global-configs#available-flags).
 
 <File name='Env var'>
 
@@ -17,4 +17,4 @@ dbt run
 
 </File>
 
-For more detailed information, read our [environment variables page](/docs/build/environment-variables)
+For more detailed information, read our [environment variables page](/docs/build/environment-variables).