feat(group-by): add grouped_by_value logic to event stores

[vincent-pochet]

Context

Some customers have requested a way to group usage fees on an invoice using an event property. The same charge model properties should be applied to each group. The logic will only apply to standard charge model.

Description

This PR refactors the filtering arguments in the events store services:

• Remove the unused event argument
• Move the group argument as a sub value of a new filters one
• Add grouped_by and grouped_by_value argument in the filters
• Add logic to handle grouped_by_value when present