Allow dynamic subscriptions in Argo CD source plugin

[chrislwade]

Overview

Update Argo CD source plugin to dynamically subscribe to newly created Argo CD Applications without requiring a configuration change or plugin restart. This could be implemented via selectors and annotations or allowing name within the existing static configuration to be a regular expression.

Acceptance Criteria

• PREFERRED: Add app selector based configuration for defaultSubscriptions.
• ALTERNATIVELY: Update defaultSubscriptions.applications[*].name to be expressed as a regular expression.
• Ensure newly created/deleted, matching, applications have subscriptions created and deleted dynamically without requiring a configuration reload.
• Make sure documentation is up-to-date, create one if needed
• Add test coverage for happy-path (unit or e2e test)

Reason

When using ApplicationSet or the app-of-apps pattern to dynamically create Applications within Argo CD itself, having to reconfigure and restart Botkube to enable notifications for newly created applications is not ideal.

[pkosiec]

Thank you Christopher for the issue. This relates to the issue #1240 as we also use app of apps approach.

Just to make sure it is archived, here's the full conversation: