Updated `EmailTemplateQuery` to use `Language` instead of `Culture` and added an explicit body. Introduced a new namespace for better organization and added `ReadEmailTemplateResponse` to provide a structured response for querying email templates, including relevant parameters.
- Updated `Constants.vb` to include new email template types:
`DocumentRejected_ADM`, `DocumentRejected_REC`, and
`DocumentRejected_REC_2`.
- Introduced `EmailTemplateQuery` record in `EmailTemplateQuery.cs`
with parameters for `Id`, `Type`, and `Culture`, along with
German documentation.
- Added `ReadEmailTemplateQuery` record in
`ReadEmailTemplateQuery.cs` that inherits from
`EmailTemplateQuery` for reading email templates.
