feat(scheduler): keep participant list in sync

[whitdog47]

This pull request introduces a new scheduled task to ensure that the participant list for incidents is kept in sync with the members of associated Slack conversations. Additionally, it optimizes Slack API calls by implementing a caching mechanism to improve efficiency.

Key Changes

1. Scheduled Task for Member Sync:

   • Added a new scheduled task incident_sync_members that runs every hour.
   • This task checks all active and stable incidents to ensure that all members of the associated Slack conversations are included in the incident's participant list.
   • If any members are missing, they are automatically added as observers.

2. Slack API Enhancements:

   • Introduced a WebClientWrapper class to ensure that Slack API client instances with the same token are treated as equal for caching purposes.
   • Implemented caching for several Slack API calls to reduce redundant requests and improve performance.
   • Added a new method get_all_member_emails to fetch all member emails from a Slack conversation, which is utilized in the member sync task.

3. Code Refactoring:

   • Refactored existing Slack API methods to use the new caching mechanism.
   • Updated the SlackAPIGetEndpoints enum to include the conversations_members endpoint.

Files Changed

• src/dispatch/incident/scheduled.py: Added the incident_sync_members function.
• src/dispatch/plugins/dispatch_slack/enums.py: Updated to include the new Slack API endpoint.
• src/dispatch/plugins/dispatch_slack/plugin.py: Added the get_all_member_emails method.
• src/dispatch/plugins/dispatch_slack/service.py: Implemented caching for Slack API calls and refactored existing methods.

Fixes DISDEV-66.

[mvilanova]

Looks good to me. Do we know why conversation and incident membership is getting out of sync?