EDS deduping endpoints with same address but different metadata

*Title*: *EDS deduping endpoints with same address but different metadata*

*Description*:

When testing LB behavior and config_dump?include_eds for an EDS cluster with endpoints that have the same address, but different metadata I see that only one endpoint is actually preserved. This behavior makes sense to me, but I can't find documentation that says it should be happening. Assuming it's not correct, the goal is to send traffic to the same internal listener and then using a custom filter on that internal listener extract destination info from passthrough metadata.

Notes:
* I have not tested this with socketaddress
* STATIC clusters with similar sets of endpoints seem to be ok
cc @kyessenov

*Repro steps*:

Using the static config below, and a modified [example xds server](https://github.com/envoyproxy/go-control-plane/tree/main/internal/example) that just returns endpoints for "outbound_service"

static config (admin on 15000, points to xds on 15012)

```yaml
node:
id: test-id
cluster: outbound_service
admin:
address:
socket_address: { address: 127.0.0.1, port_value: 15000 }
bootstrap_extensions:
- name: envoy.bootstrap.internal_listener
typed_config:
"@type": type.googleapis.com/envoy.extensions.bootstrap.internal_listener.v3.InternalListener
layered_runtime:
layers:
- name: global config
static_layer:
envoy.reloadable_features.internal_address: 'true'
static_resources:
listeners:
- name: outbound_capture
use_original_dst: true
address:
socket_address: { address: 127.0.0.1, port_value: 15001 }
filter_chains:
- filters:
- name: envoy.filters.network.tcp_proxy
typed_config:
"@type": type.googleapis.com/envoy.extensions.filters.network.tcp_proxy.v3.TcpProxy
stat_prefix: ingress_tcp
cluster: outbound_service
- name: tunnel_lis
internal_listener: {}
address:
envoy_internal_address:
server_listener_name: tunnel_lis
filter_chains:
- filters:
- name: envoy.filters.network.tcp_proxy
typed_config:
"@type": type.googleapis.com/envoy.extensions.filters.network.tcp_proxy.v3.TcpProxy
stat_prefix: ingress_tcp
cluster: outbound_tunnel
clusters:
- name: outbound_service
type: EDS
lb_policy: ROUND_ROBIN
eds_cluster_config:
eds_config:
resource_api_version: V3
api_config_source:
api_type: GRPC
transport_api_version: V3
grpc_services:
- envoy_grpc:
cluster_name: xds_cluster

- name: outbound_tunnel # using a custom filter to set original dst
type: ORIGINAL_DST
lb_policy: CLUSTER_PROVIDED

- name: xds_cluster
connect_timeout: 0.25s
type: STATIC
lb_policy: ROUND_ROBIN
typed_extension_protocol_options:
envoy.extensions.upstreams.http.v3.HttpProtocolOptions:
"@type": type.googleapis.com/envoy.extensions.upstreams.http.v3.HttpProtocolOptions
explicit_http_config:
http2_protocol_options:
connection_keepalive:
interval: 30s
timeout: 5s
upstream_connection_options:
# configure a TCP keep-alive to detect and reconnect to the admin
# server in the event of a TCP socket half open connection
tcp_keepalive: {}
load_assignment:
cluster_name: xds_cluster
endpoints:
- lb_endpoints:
- endpoint:
address:
socket_address:
address: 127.0.0.1
port_value: 15012
```

*Admin and Stats Output*:

I should have two endpoints, with upstream `0` and `1` in metadata

```json

"lb_endpoints": [
{
"endpoint": {
"address": {
"envoy_internal_address": {
"server_listener_name": "tunnel_lis"
}
},
"health_check_config": {}
},
"health_status": "HEALTHY",
"metadata": {
"filter_metadata": {
"tunnel": {
"upstream": 0
}
}
},
"load_balancing_weight": 1
}
]
```