Improve user experience around scope setting in config.ini

The config.ini recently gained a scope setting in the server sections. This is now mandatory. As a result, an upgraded debusine-client does not work with an old config.ini. Maybe add release notes?

The /-/user/token/ page as a config.ini template containing this:

scope = one-of-the-scopes-listed-below (or pass --scope on the command line)

This reads as if the scope setting were optional when you supply --scope, but in fact it is never optional. Consider updating the template.

Things to do:

• make scope mandatory in configuration (!1478 (merged))
• make --scope optional, and used only for testing: normal use defines one server per scope (I confirmed the code and unit tests match this expectation)
• address todo:: in docs/index.rst !1479 (merged)
• revamp our release history section !1480 (closed) !1502 (merged)
• no scope aliases at this point (note that if they are needed they are simple to implement with a settings configuration and a redirect in the middleware)