Feat: Add optional comment upon toggle action

[christophstrasen]

I as a delivery-manager or ops-conscious user
In order to allow everyone to better understand the current state of code behind a feature
I would like to provide a comment as to why I toggled a flag on or off

Acceptance-Criteria:

• I can add a comment when I toggle a flag
• I am not forced to add a comment
• I don't need to spend an extra click if I don't want to comment
• comments are exposed via the existing webhook event so that downstream systems might use it
• comments are saved alongside the toggle history
• comments are part of the toggle history API

[shanlashari]

would be very cool, if the team Laika can review the request, FYI @dbrabera