ProdOps Slackbot

Related to #4489 (closed)

This merge request adds the following files to the repository:

• lib/prod_ops_slackbot.rb: A Ruby script for a Slackbot that sends reminders based on the schedule specified in a YAML file.
• config/slackbot_messages.yml: A YAML file that defines the reminders to be sent by the Slackbot.

This MR also updates the README to include documentation for the above files and adds gem 'slack-ruby-client' to Gemfile.

The Slackbot uses the Slack API, Date, and YAML libraries to send messages to a specified channel at the appropriate time based on the schedule defined in the YAML file.

When the ProdOps Bot is approved and installed, the ENV variable will be added to this project and then this MR can be merged.

• Slackbot Approval Issue

Example

- name: Monthly OKR Reminder
  channel: "product"  # do not include the #hashtag in the channel name
  schedule:
    type: monthly  # weekly | monthly | annual
    # day_of_week: Monday  # if weekly
    day_of_month: 5  # if monthly or annual
    # month: December  # if annual
  blocks:
  - type: header
    text:
      type: plain_text
      text: ":chart_with_upwards_trend: Monthly reminder to update your OKRs"
  - type: section
    text:
      type: mrkdwn
      text: |
        Please take a few minutes to update your OKRs so we can stay on track for updating Key Review slides.