When using bash style substitution env variable in distribution
template, we are processing the string and convert it to the type
associated with the provider's config class. This allows us to return
the proper type. This is crucial for api key since they are not strings
anymore but SecretStr. If the key is unset we will get an empty string
which will result in a Pydantic error like:
```
ERROR 2025-09-25 21:40:44,565 __main__:527 core::server: Error creating app: 1 validation error for AnthropicConfig
api_key
Input should be a valid string
For further information visit
https://errors.pydantic.dev/2.11/v/string_type
```
Signed-off-by: Sébastien Han <seb@redhat.com>
bc64635835