[Lens] Formula: Time offset

[flash1293]

In the Lens formula, time offset should be configurable on a per-metric basis:
count(offset=1d)/count()

The offset should be passed to esaggs where it is split into multiple requests and merged into a single table, transparently for the rest of the logic in Lens - tracked here: #71287

We should decide whether there should also be a UI for this, allowing the user to configure a total time offset for the whole formula. In this case we would need to decide how offsets of the formula and individual metric offsets behave (adding together? overwriting?)

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[flash1293]

Fixed by #101718