Optimize announcement channels and XDS config push in osm-controller

[shashankram]

Please describe the Improvement and/or Feature Request
In the current implementation of how announcements from various components are acted upon, mesh-catalog in osm-controller implements functionality to listen for events from components (KubeController, MeshSpec, Configurator etc.) and broadcasts these events to connected Envoy proxies via XDS. All events are treated the same, which will result in performance issues where there are a large number of connected proxies being updated periodically even when they don't have to.

For example, enabling the debug server from the osm-config ConfigMap will result in generating and pushing Envoy configurations to all connected proxies, which does not make sense from a scalability and performance perspective.

Scope (please mark with X where applicable)

• New Functionality [ ]
• Install [ ]
• SMI Traffic Access Policy [ ]
• SMI Traffic Specs Policy [ ]
• SMI Traffic Split Policy [ ]
• Permissive Traffic Policy [ ]
• Ingress [ ]
• Egress [ ]
• Envoy Control Plane [X]
• CLI Tool [ ]
• Metrics [ ]
• Certificate Management [ ]
• Sidecar Injection [ ]
• Logging [ ]
• Debugging [ ]
• Tests [ ]
• CI System [ ]
• Project Release [ ]

Possible use cases
The purpose of this issue is to propose a different model to generate and push Envoy configurations to connected proxies based on more context, rather than doing so on any announcements that the catalog subscribes to.

[eduser25]

#2220, #2308 and #2086 have largely fixed this for most configmap related events (config toggles to debug server, tracing configs and whatnot).

Follow up work will address identifying delta changes on mesh-specific events (pods, services, smi, etc) and be able to propagate updates to relevant proxies, whose solution I believe will align with other performance issues open, such as #1958.

[snehachhabria]

Most of the issues related to this are already resolved (announcement channels). #1958 is a follow up