Add spanmetrics, servicegraph histogram buckets to user-configurable overrides api

[mar4uk]

What this PR does:
Extends the user-configurable overrides added in #2543 with histogram buckets override.

New JSON payload:

{
    "forwarders": [],
    "metrics_generator": {
        "processors": [
            "service-graphs",
            "span-metrics"
        ],
        "disable_collection": false,
        "collection_interval": "60s",
        "processor": {
            "service_graphs": {
                "dimensions": [
                    "service.namespace"
                ],
                "enable_client_server_prefix": true,
                "peer_attributes": [
                    "peer.service",
                    "db.name",
                    "db.system",
                    "db.url"
                ],
                "histogram_buckets": [0, 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10]
            },
            "span_metrics": {
                "dimensions": [
                    "service.namespace"
                ],
                "enable_target_info": true,
                "histogram_buckets": [0, 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10],
                "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]

[CLAassistant]

All committers have signed the CLA.

[yvrhdn]

Thank you for your contribution, this is looking good! I've just merged in the latest changes from main and fixed a typo.