[Doc] Rewrite auth guide for the provider (#4739)

## Changes
#4688 identifies a gap in the documentation for authentication in the
provider that can be confusing for new users, specifically that there is
no description of how to set the `host` argument for account-level
usage. This PR adds this section, listing all supported account-level
hosts. Additionally, I have reorganized the page, consolidating the
arguments & environment variables into the provider itself, as well as
prioritizing OAuth-based auth methods above PAT token or those requiring
long-lived secrets.

## Tests
N/A.

---------

Co-authored-by: Alex Ott <[email protected]>
Co-authored-by: vuong-nguyen <[email protected]>

Author: 3 people

NEXT_CHANGELOG.md

@@ -16,9 +16,9 @@
 
 ### Documentation
 
+ * Improve the landing page documentation to prioritize preferred authentication methods and provide better guidance on how to configure the `host` argument.
  * Mark GKE-related fields for `databricks_mws_workspaces` and `databricks_mws_networks` as deprecated([#4752](https://github.com/databricks/terraform-provider-databricks/pull/4752)).
 
-
 ### Exporter
 
 ### Internal Changes