Customize block page greet to include the user's name

[jennifertsai]

Description

We want to include the user's name in the onboarding and in the blocker greeting: "Hey Jennifer! reflect"

Acceptance Criteria

• Get the user name from Chrome browser API and store it in a variable https://stackoverflow.com/questions/28980582/chrome-extension-how-to-get-user-name
• Display the name on the onboarding screen and blocker greeting