feat: improve UI for timespan inputs on admin page (#726)

* Define Timestamp type

* Implement Timestamp utils

* Implement Timespan input

* Use timestamp input on config page

* Add timespan type to config services

* Refactor maxExpiration to use timespan type across services and components

* Update sessionDuration to use timespan type in config and adjust token expiration logic

* Update localized strings

frontend/src/types/timespan.type.ts

@@ -0,0 +1,2 @@
+export type TimeUnit = "minutes" | "hours" | "days" | "weeks" | "months" | "years";
+export type Timespan = { value: number; unit: TimeUnit };