Upgrade react announcements & reimplement announcement component with Fluent UI v9#1541

Sandeep-FED wants to merge 4 commits intopnp:mainpnp/sp-dev-fx-extensions:mainfrom

Sandeep-FED:upgrade-reactAnnouncementsSandeep-FED/sp-dev-fx-extensions:upgrade-reactAnnouncementsCopy head branch name to clipboard