Flag/Report Channel

Following: https://gitlab.cern.ch/push-notifications/notifications-design/-/issues/19 Add a button to flag/report channel on the channel list.

Should also be on the channel view.

Should pop up an option menu to select the reason for the report:

• Misused category/subcategory/tag
• Inappropriate name
• Inactive/Dead channel
• Other.

Suggestions: https://react.semantic-ui.com/collections/menu/#content-dropdown-item

Then a modal for Confirming the report.