[FEAT/CHORE]: Add datetime to global system default prompt

[timothycarambat]

What would you like to see?

When I make a workspace or am using the global default prompt we should be injecting {datetime} to prevent model hallucinations during tool calls and general chatting.

The small amount of tokens should have very little impact.

[Adityai1411]

I'd like to work on this. I understand the change as adding {datetime} support to the global/workspace system prompt interpolation so chats/tool calls receive the current date/time at request time.