v0.9.2: Allow handling of study-reminder emails

Added

• Email templates can use the language attribute that would contain the preferred language from the user model. Example usage added to the docs.

Changed

• "Auto email" definitions can contain a label, so that admins can describe the intent for the specific config.
• Updated dependencies (reflected in go.mod).
• Email-templates documentation includes new possibilities related to the above changes of this release.