Theme.toml [extra] config aren't loaded when developing a theme

[bitinn]

Bug Report

I am developing a theme, but Zola doesn't read the root directory's theme.toml[extra] while serving; I have to manually copy the same variables into config.toml [extra], in order for templates to read config.extra.xxxxxx properly.

Environment

Zola version: zola-v0.21.0-aarch64-apple-darwin

Expected Behavior

It would be great to read the default value from theme.toml when we are developing a theme.
(An option to read multiple toml might also work.)

Current Behavior

theme.toml [extra] config has no effect on a site.

Step to reproduce

1. zola init theme-name
2. add theme.toml and a [extra] section with a custom variable
3. try to read this value in template without declaring in config.toml

The doc made it sound like theme.toml extra are merged with config.toml extra, but instead theme.toml extra aren't used.
https://www.getzola.org/documentation/themes/creating-a-theme/