Expose GCP Secret Manager case sensitive option

[bellmatthewf]

Issue 625

Issue
The "pydantic-settings[gcp-secret-manager]" integration does not expose the case_sensitive parameter in it's API. It defaults to True and cannot be changed.

class GoogleSecretManagerSettingsSource(EnvSettingsSource):
    def __init__(
        self,
        settings_cls: type[BaseSettings],
        credentials: Credentials | None = None,
        project_id: str | None = None,
        env_prefix: str | None = None,
        env_parse_none_str: str | None = None,
        env_parse_enums: bool | None = None,
        secret_client: SecretManagerServiceClient | None = None,
    ) -> None:
        
        ...

        super().__init__(
            settings_cls,
            case_sensitive=True,
            env_prefix=env_prefix,
            env_ignore_empty=False,
            env_parse_none_str=env_parse_none_str,
            env_parse_enums=env_parse_enums,
        )

Note on changes
I considered using the parse_env_vars util function to keep this source in line with others, but that function isn't ideal here because it would iteratively call the GCP API during instantiation to get each variable value.

Better to keep those calls lazy by implementing case sensitivity changes at the mapping class level

[hramezani]

Don't we need to define a default value for case_sensitive for backward compatibility?

[bellmatthewf]

Users should never be instantiating this class directly. The GoogleSecretManagerMapping class is only instantiated internally within the GoogleSecretManagerSettingsSource class.

I added a default value to the new case_sensitive parameter of that class which will carry through to here.

[ezwiefel]

@bellmatthewf - That makes sense to me.

[hramezani]

Thanks @bellmatthewf for this PR.

@ezwiefel Can you take a look at this PR?

[ezwiefel]

@bellmatthewf - That makes sense to me.

[ezwiefel]

@hramezani LGTM

[hramezani]

Thanks @bellmatthewf for the PR and @ezwiefel for review.