Elex Test Calendar Bot: Update Slack message

[abidishajia]

Currently, the message being sent to Slack is generic.

Update sendMessageToSlack function so it sends the correct information. As Aly mentioned in this ticket, the format would be something like this:

AP: Customer Testing begins now — PA Presidential/State Primary (4:30pm-5:30pm)
AP: Election Day — PR Dem Presidential Primary
To check if everything is working as expected, check it on staging here: [dynamic URL for that state]