Event streams can't be created when public_base_url is not defined

It seems that `public_base_url` has no default value and the documentation does not say that it must be defined, so if the application is installed without defining that variable event streams can not be created, the application returns an error like: `EventStream of type Token Event Stream cannot be used because EVENT_STREAM_BASE_URL is not configured. Please check with your site administrator.`

The documentation should indicate that the variable must be defined in order to work with event streams or it should have a default value.

This issue has been reported in the forum. [Ref](https://forum.ansible.com/t/some-help-for-newbie-event-stream-base-url-is-not-configured-in-eda/39501/1).

No file or test is named. Start by locating the documentation and configuration definition for public_base_url, then determine whether the documented requirement or a default is intended; done means event streams can be created after following the documented setup.

Written by the indexing model from the issue text.