[REQUEST] Last week's Slack report should account for local holidays

[etagwerker]

Before we start...:

• I checked the documentation and didn't find this feature
• I checked to make sure that this feature has not already been requested

Branch/Commit:

main branch.

Problem:

As a supervisor
I want to get last week's report and see a note about local holidays per person
So that I can understand if there were local holidays last week or not

Resources:

This feature is blocked by #110

The project is already using the holidays gem: https://rubygems.org/gems/holidays

I will abide by the code of conduct