Make message timestamp format configurable

[Haarolean]

We changed default date format as requested in #2162.

We need the datetime format configurable on the frontend for the ones who prefer the US format or anything else.

[Haarolean]

frontend requirements: #2566

[sarkarshuvojit]

Hey @Haarolean I would like to take this up. Do we want to give the users a limited set of predefined formats, or do we want to give them full flexibility to input a date format which we can use to safely parse any date to?

[sarkarshuvojit]

I think giving them a limited set of formats will be better as we will reduce uncertainty at runtime. And, that set of formats can come from a standard set of formats used around the globe.

We can also do a hybrid, where we provide a few standard formats & also let the user input their own format as text input. To reduce complexity we can parse and validate that date format and provide an appropriate error to the user.

[Haarolean]

Discussed on discord: needs discussion

there are a few problems with this one:

1. we don't have a design solution for that one, yet
2. Not sure that we'd need this any longer since we implemented a dynamic timestamp format depending on the users' locale (US vs non-US), which looks like it's enough for now

[danielgafni]

It would be useful if more granular (sub-second, like milliseconds) timestamp information could be displayed too