Add span metrics filter policies to user-configurable overrides api

[rlankfo]

What this PR does:

Extends the user-configurable overrides added in #2543 with spanmetrics filter policies override.

New JSON Payload example:

{
    "forwarders": [],
    "metrics_generator": {
        "processors": [
            "service-graphs",
            "span-metrics"
        ],
        "disable_collection": false,
        "processor": {
            "service_graphs": {
                "dimensions": [
                    "service.namespace"
                ],
                "enable_client_server_prefix": true,
                "peer_attributes": [
                    "peer.service",
                    "db.name",
                    "db.system",
                    "db.url"
                ]
            },
            "span_metrics": {
                "dimensions": [
                    "service.namespace"
                ],
                "enable_target_info": true,
                "filter_policies": [
                    {
                        "include": {
                            "match_type": "strict",
                            "attributes": [
                                {
                                    "key": "span.kind",
                                    "value": "SPAN_KIND_SERVER"
                                }
                            ]
                        }
                    },
                    {
                        "include": {
                            "match_type": "strict",
                            "attributes": [
                                {
                                    "key": "span.kind",
                                    "value": "SPAN_KIND_CLIENT"
                                }
                            ]
                        }
                    }
                ]
            }
        }
    }
}

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[yvrhdn]

Thanks!