message: cincinnati: support templated values in base URL
  This adds support for simple templated variables substitution on
  Cincinnati base URL.
diff: @@ -28,11 +28,16 @@ impl Cincinnati {
  bail!("empty Cincinnati base URL");
  }
  - // TODO(lucab): add envsubst
  - let _env = id.url_variables();
  - let c = Self {
  - base_url: cfg.base_url,
  + /// Substitute templated key with agent runtime values.
  + let base_url = if envsubst::is_templated(&cfg.base_url) {
  + let context = id.url_variables();
  + envsubst::validate_vars(&context)?;
  + envsubst::substitute(cfg.base_url, &context)?
  + } else {
  + cfg.base_url
  };
  +
  + let c = Self { base_url };
  Ok(c)
  }
  