Members can leave a testimonial

Description of the issue 📄

A member that has attended more than X events and has no testimonial associated with them can leave a testimonial

• Add controller and related view so that a new member can add a testimonial
  • Add some text to inform members that any testimonial along with their name and profile picture might be used for the promotion of codebar (website, prospectus, etc)
  • Only allow for one testimonial per member
  • Once testimonial is created the page should no longer be available to member (or maybe a read-only version only can be available)
• Extend testimonial model to have public boolean field
• Add rake task to update existing testimonials to public
• Add admin/testimonials#index page
  • List all testimonials, with member name, text, current status and actions columns
  • Enable admins to toggle the status
  • Only available to users with the admin role
• Update main page testimonials query to only retrieve public testimonials - https://github.com/codebar/planner/blob/master/app/controllers/dashboard_controller.rb#L17

To do 📋

• Claim this issue (comment below, or assign yourself if you are part of the codebar org)
• Fork and clone the repository
• Update the relevant files. Follow the steps to fix section in this issue.
• Commit your changes as one commit. Use the title of this issue as your commit message
• Submit a pull request
• Mention this issue in the PR description by including it's number
• Have your pull request reviewed & merged by a codebar team member