Implement proper time handling and estimation

[PatrickKa]

Description

We need a time library that provides functions to get the current Rodos time (= time since last reset) and the estimated real time (= UTC), to store the time in the persistent state, and to update it when a command is received.

I propose a NamedType called Timestamp that is an int32_t under the hood, for all this. Also, the real time offset should be a topic that gets published by the real time thread and used by the functions getting the current real time. However, updating the offset is then nontrivial since topics can only have a single publisher, but the update function also wants to change the offset.

Edit: We use the strong types from #320, and I don't think that we need a topic for things like the time offset if we already store it as a persistent variable and Load() and Store() will be "atomic". Also, I think that the simple functionality of storing the time offset does not need a separate real time thread. We can just do that in the telemetry thread, where we need to touch all persistent variables anyway.

To do

• Add strong types for time #320
• Add functions to get current Rodos and real time #221
• Regularly store real time and real time offset #222
• Add function to update real time estimation #223