Add more flexibility in absent username extraction

[remi]

📖 Description and reason

Recently, Absence.io changed how it exposes absences as calendar events. Previously, each event title was formatted like this:

Out of Office - $NAME

but now the absence type is used as the prefix instead of a generic one, so we have:

Vacation - $NAME
Maternity Leave - $NAME
etc.

We want to support all of them 🙂

👷 Work done

Tasks

• [x] Remove the hardcoded Out of Office prefix and use only the last part of the title as the name
• [x] Update test suite

🦀 Dispatch

#dispatch/elixir

[mirego-builds]

🦀 Requesting reviewers for this pull request:

• @JoeyBG (contributor with 0 commits in the last 90 days and 1 commits overall)
• @MathieuLegault1 (reviewer for the elixir stack)