Fold POSTHOG_SELF_HOSTED into POSTHOG: one provider now covers Cloud (OAuth + region-pinned API key) and self-hosted (API key + instance URL), since both already share the driver, name resolver, and PostHogConnectorSettings{BaseURL}. The API-key form picks a deployment (Cloud US/EU or self-hosted URL); the resolver requires exactly one of region/instanceUrl.
Drop the POSTHOG_SELF_HOSTED enum value, registration, migration, and logo mapping. Extract the deployment selector into a dedicated PostHogDeploymentField component. Point the driver tests at us.posthog.com instead of the legacy app.posthog.com host.
Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>