[BB-8588] Add reminder options to report

This PR adds the following options for sending reminders to users who have not completed the checklists on time:

1. Send via Email option that launches an email client with the 'To' field populated with team members emails.
2. Copy @mentions option that copies the usernames prefixed with @ in the clipboard. It also updates the text Date sent to Date created.

Supporting information

• Jira ticket: BB-8588
• GitLab issue: #131 (closed)

Visual changes

• Screenshots

Options icon shows up at the end of each row in the overview report:

Dropdown options when the icon is clicked:

Email client started with To field populated with required email addresses:

Usernames copied to clipboard when Copy @mentions option is clicked:

Testing instructions

1. Setup devstack and enable one of the default checklists. Wait for a couple of runs to pass.
2. Go to reports section and verify that the options icon shows up for each row.
3. Verify that clicking on the Send via Email option starts the default email client with the To field populated with the email addresses of the users who have not responded to the checklist.
4. Verify that clicking on the Copy @mentions option copies the usernames to the clipboard by pasting on a different page.

Author notes and concerns

None