prefect-dbt - update integration docs

[seanpwlms]

Documents new features introduced in 0.5.0 and reorganizes content for clarity.

Example

Checklist

• This pull request includes a label categorizing the change e.g. maintenance, fix, feature, enhancement, docs.
• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• If this pull request adds new functionality, it includes unit tests that cover the changes
• If this pull request removes docs files, it includes redirect settings in mint.json.
• If this pull request adds functions or classes, it includes helpful docstrings.

[seanpwlms]

Thanks for the feedback, @billpalombi

[billpalombi]

One final nit but this lgtm